CHORDATE ZOOLOGY – LAB 1:
NON-VERTEBRATE AND PRIMITIVE VERTEBRATE CHORDATES
Part I: Non-Vertebrate Chordates
The Phylum Chordata includes 3 subphyla: Urochordata, Cephalochordata, and Vertebrata. Part I of his lab will introduce you to the non-vertebrate chordates and their closest living relatives, the Hemichordates. You will also learn which features (characters) define each group. The information you learn will be essential to understanding the evolutionary and taxonomic relationships to be discussed in lecture. You will examine the following material:
1) Hemichordates: whole specimens (genus Dolichoglossus or Balanoglossus); a demonstration slide of a sagittal section (of Balanoglossus).
2) Urochordates: whole specimens of Corella to dissect; a demonstration of a Ciona dissected; Molgula in lucite blocks; slides of tunicate larvae.
3) Cephalochordates: whole specimens of amphioxus; slides of whole and cross sectioned amphioxus.
After reviewing pages xi-xii, follow the directions on pages 1-15 in the manual. The Ciona and tunicate larvae are not described in detail in the manual, but study the slides using the diagram (fig. 1-2C) as a guide. As you observe the specimens, fill in the chart by putting a check in the appropriate box if the character is present in the group at ANY time during ontogeny (development). Remember that a characteristic feature may be evident in a larva but not in an adult. Use what you know about yourself and the lamprey (Part II of this lab) to fill in the vertebrate column. Use the chart and insights about yourself (you are a vertebrate) to answer the following questions.
Dorsal Hollow Nerve tube
Post Anal Tail
1) Explain why the Hemichordates thought to be closely related to chordates, but are not considered to be true chordates?
2) Why are Cephalochordates and Urochordates considered true chordates?
3) Which of these two groups do you think is most closely related to the vertebrates? Explain why?
Part II: The Lamprey, A Primitive Vertebrate
Reading: 16-28, all figures.
You examined two subphyla of the Chordata in the first part of this lab. In the second half you will study the lamprey, a member of the Class Agnatha which includes the most primitive vertebrates. The word "agnath" means jawless; other types of vertebrates have developed true jaws. Remember that the lamprey is merely a member of this primitive group of fish, and that the lamprey itself should not be thought of as the actual ancestor to the jawed vertebrates. The lamprey is in fact very specialized as a fish parasite, and simply has evolved different specializations than jawed fish. We will examine it because it is a readily available example of an agnath.
This is our first vertebrate, so think about the chordate characters you have just learned. Also be aware of the characters that unite the vertebrates. Examine the skeleton in the glass tube, and make sure you understand the arrangement of the branchial arches. These will become VERY IMPORTANT in the weeks ahead! Many features of the lamprey will be seen again throughout the semester, so it will help to start becoming familiar with them now. In addition, take note of the very specialized characters present in the lamprey.
Materials: There are not enough lampreys for each pair of students to dissect. The preserved specimens are already cut in sagittal and cross sections; they are in buckets on each table for students to share. There are also lamprey sections embedded in lucite blocks. You should observe the large ammocoete larvae specimens in jars (juvenile lampreys) and the small ones on slides. Also study the lamprey skeleton.
1) How have the chordate characters been changed in the vertebrates? The notochord, nerve tube, and endostyle have been modified in significant ways. How?
2) In the ADULT Lamprey the gill slits have changed their primary function. Explain how the old and new functions are now separated?
3) What are the new vertebrate characters present in the lamprey?
4) In what ways do the juvenile lamprey look more like the non-vertebrate chordates you saw in Part I of this lab? Why do you think this is true?
5) What are some of the specializations seen in the adult lamprey, what roles might they play in this animal’s current ecology?
LAB 2: CRANIAL SKELETAL SYSTEMS
PLEASE BE GENTLE WITH SKELETAL MATERIALS –
MANY ARE FRAGILE AND/OR EXPENSIVE!
The first week of this laboratory will compare the head skeletons of several vertebrates. Next week we will look at the mammalian cranial skeleton and post cranial axial systems of all representative vertebrates. The final week of skeletal systems we will look at the appendicular system. While looking at the structures, think about their evolution and embryonic origins. You should know from your reading the difference between the chondrocranium, visceral, and dermal bones, and should make sure that you know what type of bone you are looking at.
This is a comparative exercise, so you should also consider the relationships between groups! You should learn what characters are primitive and which are specialized, and make sure you know the homologies between bones of different groups. Color coding the figures in your lab book might help you in this. Keeping a chart of characters and homologies is also a good idea. There is one in the lab book for the tetrapods. Readings: 29 - 39, 52 - 83; all figures.
Follow the lab manual but also note these major points:
LAMPREY – Review: 1) The chondrocranium is not ossified. 2) The visceral skeleton is a continuous unit of cartilage. Visceral arches (branchial basket) are joined to each other and to the chondrocranium. The arches are all branchial – no jaws! 3) There are no dermal elements.
GNATHOSTOMES – FISHES
SHARK – 1) As the lamprey, there is no ossification of the visceral and axial skeletons. This is a derived, rather than primitive, character state in the sharks. 2) The two anterior branchial arches are specialized as jaws, while the other arches are branchial in function. Note the gill rakers and gill rays on the posterior arches. 3) Each branchial arch is divided into three parts – the basibranchial, ceratobranchial, and epibranchial. These are then modified in the anterior visceral arches to form the jaws. (see lab manual). 4) Note that the palatoquadrate of the shark articulates with the chondrocranium loosely and is supported by the hyoid arch. This is referred to as hyostylic jaw suspension.
AMIA (Bowfin) – 1) The chondrocranium is well ossified (i.e. the chondrocranial cartilage has been replaced by bone). This chondocranium is covered by heavy dermal plates. 2) As in the shark, the posterior visceral arches are branchial in function. 3) Jaw suspension is hyostylic. The caudal portion of the palatoquadrate has been ossified to form the quadrate, and the caudal portion of the mandibular cartilage has been ossified to form the articular bone…these two bones form the hinges for the jaw. 4) There are seven different series of dermal bone: dermal roof series – covers the chondrocranium; marginal jaw series – laterally covers the palatoquadrate, bears teeth; palatal series – ventrally covers the palatoquadrate; lower jaw series – covers most of the mandibular cartilage; opercular series – laterally covers posterior visceral arches; gular series – ventrally covers posterior visceral arches; pectoral series – laterally covers portions of the pectoral girdle.
PERCH –1) Similar to Amia, except that the hyomandibular cartilage is ossified to form the hyomandibula. Dermal series are grouped as in the Bowfin, although homologies with other fishes or tetrapods is uncertain. Don’t be confused by the branchial skeleton, which in some specimens has been removed and mounted below the head.
GNATHOSTOMES – AMPHIBIANS
In the tetrapods, the gular and opercular series of dermal bones disappear. Others are present, but are modified and generally simpler.
NECTURUS – The Necturus is unlike most amphibians in that it is paedomorphic – it retains many juvenile features as an adult, including external gills and a partially unossified skeleton. 1) Chondrocranium is primarily unossified, as the adults preserve the embryonic condition. The exoccipitals each bear an occipital condyle which articulates with the vertebrae. 2) Only part of the visceral arches are ossified. The palatoquadrate has been ossified to form the quadrate, but the mandibular cartilage remains as cartilage. The hyoid arch has ossified to form the stapes, which is unique to the tetrapods and carries vibrations to the inner ear. The remaining four visceral arches are largely unossified and comprise the hyoid apparatus. 3) Jaw suspension is autostylic, as the palatoquadrate articulates on its own process, rather than being supported by the hyoid arch, which forms the stapes. The hyoid apparatus functions to support the tongue and larynx 4) The dermal bones have been simplified compared to fishes, and are few in number. This is true of "higher" tetrapods as well.
GNATHOSTOMES - REPTILES
ALLIGATOR – 1) The visceral arches are similar to Necturus except that the mandibular cartilage forms an articular process of the dentary, rather than a hyomandibular, and the third and fourth arches form the bony hyoid apparatus (which you won’t be able to see). This is also true of other reptiles. 2) There is only one occipital condyle. 3) The dermal bones are more complex than in the necturus. Reptiles are classified, in part, on the number of temporal openings in the skull. The alligator is a diapsid (like the dinosaurs) as there are two temporal openings formed by the squasmosal and preorbital. 4) There is a secondary palate, formed by extensions of the palatine, maxilla, premaxilla and pterygoid. This separates the nasal and bucal (mouth) cavities so that the organism can eat and breath at the same time.
SEA TURTLE – 1) Similar to alligator except that the dermal bones are simplified, and some are missing. The turtles are anapsids… they have no temporal openings.
Below is a chart which shows the fate of the visceral arches:
ARCH SHARK FISHES AMPHIB. REPTILE MAMMAL
MANDIBULAR--> Palatoquadrate --> Quadrate ----------> Quadrate ------------> Quadrate --------> Incus
(First) Mandibular ------> Articular -----------> Articular -----------> Articular proc. ---> Maleus
HYOID -------->Hyomandibular --> Hyomand.--------> Stapes -----------> Stapes -----------> Stapes
(Second) Basihyal --------> Hyod Arch
Ceratohyal -----> Hyoid Arch Hyoid Apparatus
BRANCHIAL -----> Functional Branchial Arches
(3rd – 7th)
Questions to ask yourself:
1) What happens to the other parts of the skeleton? Try making a chart like the one above, noting what happens to the following elements: Shark chondrocranium – ethmoid and occipital regions. Fish dermal bones – ROOF: median series, temporal series, circumorbital series. PALATAL, MARGINAL and LOWER
CHORDATE ZOOLOGY – LAB 3:
AXIAL SKELETAL SYSTEM
Last week you examined the cranial skeletons of several vertebrates and studied the evolution of the visceral skeleton (from the original branchial function to forming the jaws and middle ear), the chondrocranium, and the dermal bones. This week you will study the mammal skull and the post cranial portion of the axial skeleton – the vertebral column. Once again you should treat this as a comprehensive exercise and consider the evolutionary relationships among groups. Reading: 79 – 110: all figures except 5-6; Review 53-79.
CRANIAL SKELETONS CONTINUED
CAT AND HUMAN
1) The chondrocranial, cartilage replacement bones are well developed and numerous. Mammals have two occipital condyles.
2) The visceral skeleton is reduced. The quadrate becomes the incus and the articular the maleus. These two bones plus the stapes make up the middle ear.
3) Dermal bones are well developed. The occipital and temporal (combinations of several elements) are unique to mammals.
4) Mammals are modified synapsids: they have only one temporal fenestra.
We certainly did not expect you to know everything about the cranium for the first Quiz because you had not yet studied the mammal skull. The second Quiz will cover the whole skeletal system. Concerning the cranium, you should concentrate on: types of jaw suspension; different type of bone; ossification, fusion, or loss of certain elements; the secondary palate, choanae, and nares; temporal fenestrae (anapsid, diapsid, synapsid); Lampre and Shark: components of the visceral skeleton and regions of the chondrocranium; Bowfin: the 7 dermal series, endochondral elements; All tetrapods: what happens to the original elements of the visceral skeleton (homologies), identities of dermal bones. Remember, this is again a comparative exercise.
YOU SHOULD ALWAYS KNOW WHATEVER IS COVERED IN YOUR LAB HANDOUTS; THE INFORMATION WILL MAKE MORE SENSE IF YOU DO THE LAB EXERCISES IN THE MANUAL SYSTEMATICALLY.
POSTCRANIAL AXIAL SKELETON
The post cranial axial skeleton consists of the vertebral column and ribs, all of which are endochondral bone. You will see the basic structure in the shark, and great modifications in the mammal. Necturus is intermediate.
LAMPREY: Remember from Lab I: unlike other vertebrates you will examine, the lamprey does not have fully developed vertebrae. The notochord provides the primary support and attachment of the myomeres. The spinal cord is protected only by rudimentary cartilaginuous blocks called arcualia, which are precursors to the vertebral arches of the vertebrae.
SHARK: Look at vertebrae in lucite cross and sagittal sections and full skeletons.
1) Once again, the vertebral column is not ossified in the shark, a cartilaginous fish. The vertebral arches have evolved to protect the spinal cord (which lies in the vertibral canal), and there is only a remnant of the embryonic notochord persisting in each vertebral arch and vertibral body. Ribs are dorsal.
2) Shark vertebrae are differentiated into only two types: trunk and caudal. Both consist of a vertebral arch and vertebral body (or centrum), the caudal vertebrae also have a hemal arch. This arch forms the hemal canal, which contains the caudal artery and vein.
PERCH: The vertebral column of the perch is similar to the shark’s except that it is ossified. There are spaces between vertebrae to allow flexibility. This is unnecessary in cartilaginous fishes because the cartilage itself is flexible.
NECTURUS: 1) As in the shark, the vertebral column is differentiated into trunk and caudal vertebrae. The first vertebra (the atlas) lacks ribs and is specialized to articulate with the skull. A single sacral vertebra is modified to support the pelvic girdle.
2) Ribs are dorsal, and do not appear to be homologous to those of the perch or other fishes. The ribs are short, and are not connected by a sternum, which is present in most tetrapods. This is characteristic of living amphibians, although a functional sternum may have been present in ancestral amphibians.
3) On trunk vertebrae, a small spinous process projects caudally from the dorsal region of each vertebral arch, and two pairs of zygapophyses – cranial and caudal – project laterally from each arch. Muscles attach to the spinous processes, and zygapophyses allow adjacent vertebrate to articulate with each other.
CAT AND HUMAN: 1) The vertebrae of the mammals are more highly modified than those of Necturus. Note the variation in the spinous processes and various transverse processes (which project ventrolaterally). You may see different names for the transverse processes, such as pleurapophysis or diapophysis, depending on the origin and function, but you do not need to know these names.
2) There are five major types of vertebrae: cervical, thoracic, lumbar, sacral, and caudal. Cervical: these include the atlas and axis, which are present in birds and reptiles as well, and are modified to articulate with the skull. The remaining unmodified cervical vertebrae each possess a transverse foramen through which blood vessels pass. Trunk: the trunk vertebrae include thoracic vertebrae which articulate with ribs, lumbar vertebrae which have large transverse processes but no ribs, and a sacrum which consists of several vertebrae fused together to support the pelvis (3 in the cat, 5 in the human). Caudal: the caudal vertebrae of the cat retain only a vestige of the hernal arch seen in the shark and other fishes. The human tail is vestigial.
3) The ribs unite with a segmented sternum by costal cartilage – either directly or by first uniting with cartilages from other ribs.
QUESTIONS TO ASK YOURSELF
1) Why are the vertebrae of tetrapods so much more complex than those of the fish? How is the basic structure modified? What are all the elaborate processes for?
2) What are the functions of the atlas and axis? What movements can mammals do that Necturus cannot?
3) The basic structure of the vertebra is the centrum with an arch above and below. What do the two arches protect? How does this structure change as you compare the sharks to mammals?
4) What is the significance of the temporal fenestra? What possible roles does it play in the evolution of the vertebrate skull? How are these structures used in understanding the history and classifying the different vertebrate groups?
CHORDATE ZOOLOGY – LAB 4:
APPENDICULAR SKELETAL SYSTEM
This week you will finish the skeletal systems by examining the remaining portions of the skeletal system with an emphases on the limbs. Most of the bones which make up the appendicular skeleton are endochondral in origin. The exceptions are those derived from the pectoral dermal bones of fishes, which you saw in the bowfin. While looking at these skeletons, think about how they are designed for particular functions. The limbs are modified for different types of locomotion.
READING: 111-132; Know figures 6-2; 6-3; 6-4; 6-7; 6-8a,c; 6-9; 6-10; 6-12 to 6-19. Also review pages 44, 47-48 and figures 3-6 and 3-9.
LAMPREY: no paired appendages!
SHARK: Refer to lab manual for description of shark limbs. The appendicular skeletons of sharks and most fishes are either cartilage or cartilage replacement bone. Associated dermal bones can be seen in the pectoral girdle of some primitive fishes like the bowfin.
BOWFIN: Note that the pectoral girdle is fused to the skull by dermal bone, primarily the cleithrum.
NECTURUS: 1) The basic tetrapod limbs and girdles are now present. (These did NOT evolve from the ray fin fishes we have examined, as you will learn in lecture). Note that Necturus has lost the first digit on the fore and hind limbs.
2) only parts of the appendicular skeleton are ossified. The cleithrum and clavicle persist on the pectoral girdle as the only remnants of dermal bone
3) Posture is not upright.
CAT AND HUMAN: 1) You are probably already familiar with the bones of the legs, feet, arms and hands. If not, memorize them now. These bones remain constant throughout the tetrapods although some may be lost or fused in adults of some groups. (the extreme case is the snake, which loses the limbs entirely).
2) Notice the enlargement and strengthening of the pectoral and pelvic girdles for terrestrial life.
3) The only dermal bone retained in the mammalian pectoral girdle is the clavicle. The coracoid has fused to the scapula, forming the coracoid process.
BAT AND BIRD: Wings: note that although both bats and birds have the basic tetrapod limb structure, it is modified for flight in two different ways. Also note the modification of the pectoral girdle of the bird for attachment of the flight muscles (in the whole skeleton).
COW: The cow is an artiodactyl (even toed ungulate) whose mode of locomotion is referred to as unguligrade. (Horses are perissodactyls and walk on one toe).
NOTE: you should be able to distinguish carpals, tarsals, metacarpals, metatarsals, and phalanges as SETS of elements. Among these group of bones, the only individual bones you should know are the TALUS and CALCANEUS.
For the second Quiz concentrate on: the handouts; types and parts of vertebrae in the lamprey, fish, Necturus, and mammals; basic elements of pectoral and pelvic girdles, the forelimb, and the hind limb in all the above animals you examined. Remember to go back over the materials in Lab 2 so you can compare between the mammalian skull and the skulls to the other vertebrates.
QUESTIONS TO ASK YOURSELF
1) How are these limb and girdle elements modified in the different animal groups? How are they similar? Compare the Necturus with the birds and mammals, or the pelvis of the rabbit, opossum, cat, and human. How do they change with modes of locomotion?
2) How has the appendicular skeleton of each type of animal been modified for its particular function (think primarily in terms of locomotion)?
3) Why does the radius cross over the ulna in some mammals and not others? What positional shifts of the forelimb led to this and why has the same not happened in the hind limb?
CHORDATE ZOOLOGY – LABS 5 & 6:
EXTERNAL ANATOMY AND MUSCLES
Lab 5: 29-39 background, 39-44, 133-156
Lab 6: 165-166, 167-173, 186-194, 199-205
This week we will finally begin our shark dissection; this handout is for this week and next week. MAKE SURE YOU BRING YOUR DISSECTING KIT AND A GARBAGE BAG (PREFERABLY 2) TO KEEP YOUR SHARK IN. You should first go over shark external anatomy, then begin dissection of the muscles. Next week we will complete the shark muscles and study the cat. From now on we will focus on the shark, with some comparisons to the cat. You need only read the dissection instructions for the shark, but you should read the background material on mammals each week as well. The external anatomy is fairly simple, but take the time to look at a piece of skin under a dissecting scope. Denticles are very similar teeth.
All of the muscles you will examine are voluntary, striated muscles attached either to skeletal structures (which you now know) or to superficial fascia covering other muscles. Like the skeletal system, the muscles are grouped according to embryonic origins, which correspond roughly to the parts of the body they control. (See chart on page 139-141, focusing on the shark muscles). Except for the branchial muscles, the shark muscles are simple relative to those of tetrapods, which use their limbs in a greater variety of ways. There are just two pectoral fin muscles in the fishes which give rise to the multiple deltoid and pectoral muscles seen in the mammals and the latissimus dorsi. The trapezius is homologous to the cucullaris, a visceral muscle.
DISSECTION HINTS: Muscle dissection takes some care and skill. Follow the dissection hints on p. 145 CAREFULLY, or you may destroy some of the structures. First, remove the skin and connective tissues, then try to find the rough outline of the muscle. Isolate the muscle GENTLY, separating it from other muscles using a blunt probe, closed forceps, or your fingers. Dissect the left side of your specimen, since the drawings in the manual show the left side. Leave the right side intact to dissect the respiratory system in Lab 7. Don’t just look, THINK. You might want to make a chart of origins, insertions, and function (action) for each muscle, but DON’T try to memorize it. If you can identify a muscle, you should generally be able to figure out what it’s attached to and what structure it is moving! Many of the names are based on the muscle’s action or attachment(s).
KNOW: shark – all structures listed in bold in the dissection instructions of the manual, except eye muscles (for now); cat – muscles in CAPITAL LETTERS in the chart in this handout (you will study the cat next week); UNDERSTAND: different types of attachment of muscle to bone; origin, insertion, fascia, types of actions (movements); subdivisions of the muscles.
Below is a summary of some of the major groups in the shark and cat. You should know how the muscles are grouped, the general structure and homologies, and functions. A much more detailed version of this chart is in Table 7-1.
AXIAL Hypobranchial Hyoid arch, tongue, larynx muscles
Hypaxial Muscles of ventral body wall, including
simple myomeres EXTERNAL OBLIQUE. Little remaining
segmentation. Large, sheetlike.
Expaxial Dorsal, ERECTOR SPINAE. Muscle
simple myomeres segments between vertebral processes;
fewer, longer segments than in fish
APPENDICULAR Pectoral All move limbs:
Adductor PECTORALIS COMPLEX, BICEPS.
Abductor DELTOIDS, LATISSIMUS DORSI,
Adductor HAMSTRINGS (Semitendinosus,
ADDUCTORS, SHANK FLEXORS
Abductor QUADRICEPS, GLUTEALS, SHANK
EXTENSORS, BICEPS FEMORIS
BRANCHIOMERIC Mandibular MASSETER, TEMPORALIS
(Includes adductor mandibulae, levator PQ, spiracularis,
preorbitalis, and intermandibularis in shark)
Hyoid hyoid, face, and neck muscles
Cucullaris TRAPEZIUS – associated with limb!
Superficial Larynx and pharynx muscles
(Also includes other muscles (interarcuals, branchial
adductors) generally lost in tetrapods)
***NOTE: Muscles are usually named for either their position, action, fiber direction, or shape.
Keeping these features in mind greatly facilitates remembering complicated names.
QUESTIONS TO ASK YOURSELF
1) How does the mode of locomotion of these animals affect the complexity of the muscle groups?
2) As you look at each muscle think about what skeletal elements it is moving. What is its origin and insertion?
3) Often groups of muscles will be composed of members with opposing actions. What is the significance of such groups? Does this pattern change as you move from the fish to the mammals?
QUIZ II WILL BE GIVEN DURING LAB 5 AND WILL COVER THE ENTIRE SKELETAL SYSTEM
CHORDATE ZOOLOGY – LAB 7:
DIGESTIVE AND RESPIRATORY SYSTEMS
Reading: 287-306 (shark dissection) 314-331 (skim for cat)
This week you will study the coelomic cavities, digestive organs, pharynx, and respiratory organs in the shark, and also examine them in a demonstration cat. If you finish early begin to study the hepatic portal system in your shark (pg. 341-343, picture on pg. 297) because the following week (circulation) will be busy, and the hepatic system is closely related to the digestive organs.
Coelum and Digestive System. You should understand coelom, mesentery (free sheets of tissue), visceral (on organs) and parietal (on body wall) peritoneum, and the divisions of the coelom from the background reading and diagram below (hint!). Remember that the organs do not lie in the coelom, but are "outside," covered by visceral peritoneum. Peritoneum and mesenteries make up a continuous sheet of epithelium lining the coelom. Imagine your first against and surrounded by an inflated balloon; your fist is an organ, the ballon material is visceral peritoneum, and the space inside the balloon is the coelom. The coelom forms embryonically as 2 separate cavities, separated by the dorsal and ventral mesenteries. Most of the ventral mesentery disappears, leaving a single cavity. In the adult, only the falciform ligament, lesser omentum, and a few smaller mesenteries are derived from the ventral mesentery.
Look at the mesenteries first, since they might rip while doing the rest of the dissection. Note that blood vessels run between the 2 layers of mesenteries, so DO NOT CUT OR DESTROY ANY BLOOD VESSELS in the pericardial or pleuroperitoneal cavities! You will study circulation next week. The internal digestive organs are fairly similar in most vertebrate groups. You should be able to identify them all and know their functions in the shark AND cat. You should all be able to identify them all and know their functions in the shark AND cat. You should know all structures in bold pg. 295-306; except abdominal pores, hepatic ducts, and pancreatic duct (these are hard to see). In the cat know the greater and lesser omentum, falciform ligament and all digestive organs including the caecum (where the appendix begins in humans; cats do not have one).
Respiratory System. Dissect the respiratory system on the right side (if you did the muscles on the left). DO NOT CUT THE HEART, which is ventral to the pharynx. The esophagus may be everted into the pharynx, but it can be pushed back. You should read and understand the discussion of how pressure is created in the shark pharynx. Also note that the spiracle is a reduced (vestigial) gill slit, derived from the gill slit between the mandibular and hyoid arches. In the cat you should know the divisions of the pharynx. larynx, epiglottis, tongue, esophagus, trachea, bronchi, lobes of lungs, soft and hard palates, internal and external nares, and vocal cords.
Hepatic Portal System. Before you begin looking at hepatic portal veins (all yellow) go over the discussion of general circulation patterns in fish (pg. 339-341). Note that it is essentially the same in the lamprey, but in the shark there is also a renal portal system (involving kidneys) and a hepatic portal system (involving the liver). You did not look at the hepatic system in the lamprey. A portal system is a set of veins which collect deoxygenated blood from capillaries in tissues, then takes it to a second capillary bed before returning blood to the heart (most veins return blood directly to the heart). In the hepatic portal system, deoxygenated blood from the gut goes to capillaries in the liver before returning to the heart. This is important because the liver both detoxifies the blood and stores glycogen. Thus, any ingested toxins are first collected in the gut capillaries, sent through the hepatic portal veins, and carried to the liver for immediate detoxification. If the blood returned directly to the heart the toxins would be pumped throughout the body. It is also more efficient for the digested sugars to go to the liver first.
Like many invertebrates, vertebrates are built like a "tube within a tube," having in the trunk a body cavity, or coelom, between the body wall and digestive tube. The coelom is subdivided in fishes, amphibians, and many reptiles into a pericardial cavity housing the heart and a pleuroperitoneal cavity housing most of the other viscera, including the lungs. The pericardial and pleuroperitoneal cavities in these vertebrates are separated by a fibrous transverse septum. In some reptiles and in birds and mammals the lungs occupy separate pleural cavities. The transverse septum is then supplemented by other septa including, sometimes, muscular diaphragms. In many male mammals caudal outpocketing of the coelom house the testes, and these scrotal cavities are a fourth subdivision of the coelom.
QUESTIONS TO ASK YOURSELF
1) What is the history of the coelomic cavities. Phylogenetically, how does it become more and more divided as you go across groups from the fish to the mammal? Embryologically, what are the changes that take place in the coelomic cavity as it become more and more subdivided? What are the septums and what are their origins?
2) The digestive system of all vertebrates is very similar on the gross scale (i.e. having a mouth, stomach, and intestine), but think about how they differ between groups. What are the similarities and differences between the cat and shark? Think about the complexity and metabolic differences between these two groups.
3) Gas acquisition (i.e. O2) is very important and the processes are quite different for aquatic and terrestrial organisms. What is the "double pump" mechanism seen in the shark and how does it work? What are the different types of gills and why might it be important to have a continual one-way flow of water across the gills?
4) What structures have you already seen in previous labs that are related to the efficiency of mammalian respiration and digestion?
CHORDATE ZOOLOGY LAB 8:
Reading – Background: 336-341, 367-369; Dissection: 339-357 (shark), 369-373
(cat); 389-392 (sheep heart)
This week you will complete the shark circulatory system dissection, look at the cat, and study a sheep or cow heart. Again, make sure you understand the general circulation pattern in fish and mammals, and think about what part of the body the blood vessels are supplying. Memorizing vessels isn’t worthwhile unless you also know where the blood is going and what it is carrying (hint). The dissection will be easier if you keep in mind hints in the manual (pg. 339). Understand the hepatic portal system! (Discussed in Lab 7 handout). Notice the large blue venous sinuses, and know their functions. Below is a diagram which should help you understand the major blood vessels. In general, veins are paired, though only one side is shown. Don’t be confused by the term "brachial." BRACHIAL refers to the forelimb, and BRANCHIAL refers to the fills and breathing. Brachial veins and arteries supply pectoral fins.
You should be able to find everything in bold print for the shark dissection except smaller vessels and sinuses around the head; you are required to find everything diagrammed below. Concentrate on Figures 10-5, 11-4, 11-5, 11-9, 11-12, 11-19 (basic pattern), 11-21 (heart), 11-33, 11-34; figure below. In the Cat know: heart chambers, pulmonary vessels, aorta, coronary arteries, cranial and caudal vena cava, brachiocephalic vessels, subclavians, corotids, jugulars, and. On the Sheep Heart know: same structures for cat plus auricles, pectinate and papillary muscles; tricuspid, bicuspid, semilunar valves; chordae tendineae; trabeculae carneae; moderator band.
QUESTIONS TO ASK YOURSELF
1) Why do sharks have large circulatory sinuses while mammals do not?
2) What is the "Tail Pump?" How does it work and what is its significance?
3) Can you trace the path of circulation from any given point back to that point?
For instance, from the small intestine to the heart and back to the small intestine. Which major blood vessels would be involved, which capillary systems, would a portal system be involve? Can you do this for other major areas of the body (a leg, a lung, the brain)?
4) You have already looked at respiration in vertebrates, but remember, respiration and circulation are closely linked. How are these two systems linked in tetrapods? Can you explain counter current system is involved in fish respiration?
5) How do the fish and mammal differ in terms of O2 acquisition occurs in the circulatory patterns?
CHORDATE ZOOLOGY – LAB 9
READING: READ THIS HANDOUT FIRST!!
Skim: 414-431 for mammals
(Text: 118-123, 147-149; Fig. 3-15, 3-16, 3-29)
**Besides dissecting your shark, be sure to also study the sectioned cat kidney, the pig kidneys, and the pig uterus with piglets.
This week we will dissect the reproductive and excretory system of the shark. MAKE SURE YOU LOOK AT A SHARK OF THE OPPOSITE GENDER! After dissecting your own shark, trade with someone or look at the T.A. shark to see the other gender. You should then observe the cat and the pig kidney as a comparison. Although excretory and reproductive systems are separate, they are linked in the vertebrates and may share ducts.
The ontogeny and evolution of kidney types in different groups of vertebrates is somewhat confusing, I’ll try to give an introduction here that should help you understand the manual. A NEPHRON or kidney tubule, is the functional unit of the kidney. Each nephron collects wastes at its distal end from a GLOMERULUS, which is a small capsule of arterial blood capillaries surrounded by the tubule. In taxa with a renal portal system, the tubule also passes through a bed of venous capillaries. The tubule then empties into a duct to travel to the cloaca. (More about these ducts later). There are hundreds to millions of nephrons in an individual. Generally primitive vertebrates have fewer nephrons than more advanced groups.
The nephrons are located along the mesomere, lateral to the dorsal aorta. In the embryo, the mesomere runs the entire length of the coelom. Various parts of this ridge become the functional kidney in the adults of different taxa. The terms PRONEPHROS, MESONEPHROS and METANEPHROS refer to regions of the kidney as they develop during ontogeny, although they are also sometimes used to describe adult kidneys. The pronephros is the most cranial part of the nephric ridge and is the first to develop, the mesonephros is next, and the metanephros is most caudal and develops last.
HOLONEPHROS, OPISTHONEPHROS and METANEPHROS refer to evolutionary of kidney development leading to the mammalian kidney. The holonephric kidney is the most primitive, and is hypothetical. It is assumed that the earliest vertebrates had a holonephric kidney in which the entire nephric ridge was functional in the adult.
Sharks, amphibians, and many other anamniotes, have an opisthonephric kidney. In an opisthonephric kidney, both the mesonephron and part of the metanephron are functional. The pronephron no longer has functional nephrons, but forms the ARCHINEPHRIC DUCT (Wolffian duct). The archinephric duct drains urine from the nephrons of the meso- and metanephros. In many taxa with opisthonephric kidneys, there is an ACCESSORY URINARY DUCT in males which drains the caudal part of the kidney. In males of these taxa, which include the dogfish, the archinephric duct drains only the cranial portion of the kidney. Its primary function is to transport sperm from the testes to the cloaca. In more primitive groups, the sperm are shed from the testes into the coelom, and exit through the abdominal pores. In females, the archinephric duct drains the entire kidney. The eggs are shed into the coelom and then enter the oviduct. Which is not an excretory duct.
The amniotes have a metanephric kidney in which only the metanephros is functional. In males, the kidney is drained by the URETER, which is derived from an archinephric duct outgrowth, not the accessory urinary duct. The archinephric duct is no longer attached to the kidney, and functions only in sperm transport. It is now called the EPIDIDYMIS/DUCTUS DEFERENS (vas deferens in humans). In females, the ureter is homologous to the archinephric duct, and the eggs are still shed into the coelom before entering the oviduct.
In primitive kidneys, there is one nephron per body segment. In most opisthonephric kidneys, there are multiple nephrons per body segment, but the arrangement is still linear and segmented. In metanephric kidneys, there is no longer any segmentation, and nephrons are arranged radially.
It is important to note that explaining kidney evolution in terms of this "sequence" ignores the fact that there is a different advanced kidney in the most diverse group of vertebrates, the teleosts. Many of the teleosts have a well developed PRONEPHRIC kidney derived from the pronephros of the embryo. It is drained by the archinephric duct. It is not primitive compared to the tetrapod kidney! Teleosts have a vas deferens which is not homologous to the archinephric duct.
NOTE **You should know the terms in capital letters above. You should identify all structures written in bold on pp. 405-9. Exception: It is difficult to find the accessory urinary duct. Coprodeum and urodeum aren’t important words to memorize. In the mammals you should know the ureter, bladder, urethra, sperm cord (testicular blood vessels and ductus deferens), testicle, epididymis, penis, ovaries, uterine tube, uterus, and vagina. In the sectioned kidney you should know cortex, medulla, renal sinus, papillia, pelvis, and pyramid.
QUESTIONS TO ASK YOURSELF
1) What are the primary differences between the opisthonoephros and metanephros kidneys? Which groups of organisms have each type of Kidney?
2) What happens to the archinephric duct in mammals (males and females) and what replaces them functionally?
3) Why do mammals not have a cloaca?
CHORDATE ZOOLOGY LAB 10:
SPECIAL SENSORY SYSTEMS
Reading: Lateral line system and Eyes (and muscles) 212, 216-224, 226-228 Ear and assoc.
Materials: your shark, shark and cat eye muscles, cow eyes, plastic models of the eye and ear
This week you will begin your observation of the nervous system by studying the special sense organs. These organs are special aggregations (groups) of receptor cells, which are cells that receive stimuli from the environment for transmission to the brain. Remember from our discussions of the lamprey that these organs are vertebrate characters, and most are present in the agnaths.
You will look at the gross sensory systems of your shark, including the lateral line, ampullae of Lorenzini, eyeball, external eye muscles, medial eye, nasal pouch, and inner ear. The ampullae are found only in sharks, although there are similar structures in some skates and teleosts. You will study the mammalian sensory systems by dissecting cow eyes and examining cat eye muscles and large plastic models.
You should know what kind of receptors are in each sense organ, know the function, and the overall structure. The lateral line has neuromasts, or sets of "hair cells" covered by a cupula filled with gelatinous material; it detects movements in the water. The receptors of the ear and ampullae of Lorenzini both appear to be derivatives of the neuromast. The ampullae have electroreceptive neuromasts with a single cilia. They are not covered by a cupula. (Electroreception is important in prey detection). The inner ear has hair cells covered by cupulae which are used primarily in maintaining equillibrium in fishes, but also function in hearing. Lateral eyes have rods and cones, and the nose and tongue have chemoreceptors which act as both receptors and transmitters.
Lateral line: you do not have to know individual canals. Eyeball: you should know all the structures in the eyeball dissection (from the cow eyes and model), and the external eye muscles on the shark and cat. Nose: all parts on the shark. Ear: on shark: Fig. 8-13; Fig. 8-16; on mammal: structures on plastic model and handout.
***It takes a long time and is very difficult to dissect the membranous labyrinth (shark inner ear) correctly. You should follow directions closely and think of this as a challenge. Anyone who extracts an intact membranous labyrinth from their shark WILL RECEIVE A PRIZE!
The diagram below shows the evolution of the ear more clearly than does your manual.
QUESTIONS TO ASK YOURSELF
1) Why is the lateral line system believed to be closely related to the membranous labyrinth?
2) The ampullae of Lorenzini are believed to be associated with electroreception. Describe how they function individually and how their arrangement helps with prey detection.
3) How does the tapentum lucidum of the elasmobranchs work?
4) How does the membranous labyrinth help an organism (i.e. a cat or you) maintain balance?
CHORDATE ZOOLOGY LAB 11A:
NERVOUS SYSTEM: SHARK BRAIN
Reading: 237-241 background (important), 241-257 dissection
Study Figures 9-1, 9-2, 9-3, 9-4, 9-6, 9-8; Table 9-1 (pp 252-253)
You will spend the next two weeks studying the nervous system of the shark and sheep; most of your focus will be on the brain and cranial nerves. You will learn about the nervous system as a whole, but only the brain itself is easy to see in gross dissection of the shark. You will have to memorize the cranial nerves and what they innervate in general. This is a lot of information to remember, but the functions are conserved across all vertebrates, and innervation provides important clues about homology (remember Mike’s discussion of branchial arch homology). Most of you who are going on to schools in the health professions will have to memorize the nerves at some point, so now is a good time to start. Study the chart on page 252. You should know the names and numbers of the nerves and their main branches, and generally what they innervate and whether they are sensory or motor. Don’t worry about which specific type of sensory or motor they are. Just as with muscles and blood vessels, it will be easier to learn this information if you think about where the nerves are going and why, while you dissect them.
Understand the overall breakdown and divisions of the nervous system (from the reading and your TA). Know what different types of neurons there are (i.e., sensory, motor, somatic, visceral) and that any one nerve may contain many different types of neurons.
Central NS = brain and spinal cord
Peripheral NS = nerves and ganglia
Somatic NS = innvervates skeletal muscles (1 neuron system; both sensory and motor; generally voluntary)
Autonomic NS = innvervates visceral organs, glands, smooth muscles
(2 neuron system; generally motor and involuntary)
Sympathetic NS = neurons from thoracic and lumbar regions
Parasympathetic NS = neurons from cranial and sacral regions
You should remember from the lamprey lab that the brain is a vertebrate character, and is
formed by expansion of the dorsal hollow nerve tube. Thus, the brain is hollow and filled with fluid; this cerebrospinal fluid occupies the ventricles of the brain. Primitively, and early in ontogeny, the brain is divided into three vesicles: the prosencephalon (later develops into the telencephalon and diencephalon), the mesencephalon, and the rhombencephalon (later develops into the metencephalon and myelencephalon). You will see all five of these divisions in the adult shark and sheep brains. These parts of the brain may become quite large and complex, and keep in mind the relative proportions of the regions in the shark so you can compare them to those of the mammalian brain next week. It may help to color code the regions in your lab book; you will be expected to know what region of the brain you are looking at, as well as identify specific structures. Next week you will receive more information about the function of the various regions and structures of the brain.
QUESTIONS TO ASK YOURSELF
1) What are the similarities and differences between the sympathetic and parasympathetic divisions of the autonomic nervous system? How do these two systems contrast and complement each other? What is the physical distribution of these two systems?
2) What is the blood-brain barrier? What is its function and how does it work (roughly)?
CHORDATE ZOOLOGY LAB 11B
Reading: 260-275 (top). 281-282. Reread 257-8 to review brain function of the shark.
This week you will study the brain of the sheep as a representative of mammals.
If you have not finished dissecting your shark’s brain and cranial nerves, do that first. The basic divisions and structure of the mammalian brain is the same as that of the shark, so you will already be familiar with many parts. Concentrate on the differences between the two brains; many of these are outlined in this handout. Differences primarily involve a greater emphasis (relative size or complexity) of certain regions or structures in either the shark or the sheep, resulting from their different evolutionary pathways and associated with their very different lifestyles.
Telencephalon – The most striking difference between the shark and mammalian brains is the presence of the large cerebral hemispheres in the mammal, connected by the corpus callosum. These have a thick cortex of gray matter known as the cerebral cortex, which is the "thinking" part of the brain. Voluntary motor activity is initiated here, memory is probably located here, and data for making choices is analyzed here. Notice that the surface of the cerebral hemisphere is folded into ridges (gyri) and grooves (sulci). This is true of most mammals; the shark’s cerebrum is smooth. Thus, this major integrating region (the neopallium) is greatly elaborated in mammals. The olfactory lobes of the mammal are relatively much less conspicuous than those of the shark (which relies heavily on smell), and can be seen anteroventrally.
Diencephalon – As in the shark, the mammalian diencephalon includes the optic chiasma, hypothalamus, and pituitary gland (hypophysis), which function in hormone regulation and internal homeostasis. The pituitary gland hangs from a narrow stalk (infundibulum) and is probably missing. The saccus vasculosus is seen only in fish, and may be important in regulating the pressure of fluids in the brain and spinal column in deep water. The thalamus, which relays sensory impulses to the cerebral hemispheres, is the largest division of the diencephalon in the mammals, but it is hidden by the hemispheres.
Mesencephalon – The optic lobes (rostral colliculi) are the most prominent portion of the mesencephalon in all vertebrates. In reptiles and mammals, a pair of auditory lobes (caudal colliculi) lie caudal to the optic lobes. Fish have auditory nuclei in this area, but they do not bulge from the surface. The optic and auditory lobes are collectively referred to as the corpora quadrigemina (four bodies), and can only be seen by spreading the cerebellum and cerebrum apart.
Metencephalon – The cerebellum coordinates skeletal muscles and is generally larger in tetrapods than in fishes, as it increases with increasing muscle complexity. The topography of the cerebellum is more prominent in mammals, and the pons can be seen on the ventral surface. This is the point where fibers cross from one side of the brain to the other. Like the cerebrum, the cerebellum is characterized by folds (folia) and grooves (sulci).
Brain Parts Cont.
Myelencephalon – As in the shark, the myelencephalon consists of the medulla oblongata. Reflex and visceral activities are controlled here such as heart beat and blood pressure, swimming in the shark, and breathing in mammals.
Cranial Nerves – These are the same as those of the shark (and there are two additional ones); you should be able to identify their roots (Figure 9-13).
Meninges – The mammalian brain is covered by pia mater (you can’t separate it), arachnoid, and dura mater. Cerebrospinal fluid is produced in the four ventricles of the brain by choroid plexus, and it circulates through these ventricles and around the surface of the brain and spinal cord in the subarachnoid space between the pia mater and arachnoid meninges.
*** For the nervous system, understand what is outlined in your handouts, and do the background reading)! For the sheep brain, really try to think about the major ways in which it differs from the shark brain and why. Know all the structures mentioned in this handout, and study Figures 9-12, 9-13, 9-14 (for the mesencephalon and ventracles), 9-15 (for nerves and major parts of the dimes-, and metencephalon), and 9-18. Follow the dissection instructions systematically, but you do not have to memorize everything. There are many names for internal fibres and arbitrary regions of the surface of the brain; don’t worry about these. As for the shark, concentrate on easily recognizable, definitive structures, especially those that you can compare between the shark and sheep.
QUESTIONS TO ASK YOURSELF
1) What are the 12 cranial nerves? Can you think up any good sayings to help memorize them?
2) Where is cerebral spinal fluid produced? What are some of the functions of CSF?
3) Why does the mammalian brain show such increased complexity? What are the areas of increased complexity associated with (senses? behavior?)?
4) What are reflex arcs, how do the central and periferal nervous systems integrate in such arcs?