Vertebrate Anatomy

Phylum Chordata, Subphylum Vertebrata:

In this lab, you will explore the internal anatomy of the cat, thereby gaining a better understanding of the anatomy of other vertebrates, including our own internal anatomy.

The internal anatomy of the cat is representative of the anatomy of other vertebrates and is especially similar to that of the human, more similar than other commonly dissected animals such as fetal pigs. These cats belong to our Anatomy and Physiology students and we will be just borrowing them to look at them. Thus, when you are finished, return the organs to their correct positions, close the peritoneal cavity, and wrap the skin closely around the cat. Slide the cat, head first, belly down into the plastic bag. Note that these cats are “triple-injected” — the arteries have red latex in them, the veins have blue, and the lymphatic system has yellow. Please use only a blunt probe and/or your fingers to move organs around so you don’t poke or tear anything.

Characteristics of Phylum Chordata include:

• a notochord (noto = the back; chord = string), which is present in at least all embryonic/juvenile stages (may not be present in adults of some subphyla/classes)
• a dorsal, hollow nerve cord formed by an infolding of ectoderm tissue (compare with Annelida and Arthropoda which have ventral, solid, mesodermal nerve cords)
• pharangeal slits (pharynx = throat), which originally functiond in filter feeding, but in fish became modified as gills, and in mammals as our eustachian tubes and ears
• a postanal tail (post = behind, after; anal refers to the anus), which extends beyond the anus in many taxa (thus the anus isn’t at the posterior tip of the body) — in humans, the tail is present during embryonic development but is subsequently resorbed

Characteristics of Subphylum Vertebrata include:

• an endoskeleton comprised of bones and which is able to grow along with the animal — bones are calcified in many, but not all, classes (sharks’ bones are not calcified)
• specific bones called vertebrae, which surround the nerve cord
• a definite head
• a brain enclosed within a skull
• a closed circulatory system with a ventral heart (number of chambers within the heart varies
• excretion via kidneys
• separate males and females with sexual reproduction in most (a few groups exhibit parthenogenesis and/or the ability to change sex midway through the organism’s lifetime)

More information about Phylum Chordata can be found at the Phylum Chordata page.

Safety Considerations:

Due to the toxic chemicals (of course they’re toxic — they kill bacteria, don’t they?) used to preserve these cats, these safety precautions need to be observed:

There was a problem in the past with an unexpected “squirt” of preservative liquid landing in the eye of a student who was not wearing goggles. Trust me, you do not want to have to go through the ordeal of being subjected to the eyewash station (and hospital emergency room) just for that. WEAR GOGGLES when examining the cats. If you do need to temporarily remove the goggles to draw/write in your lab notebook, do not touch, move, prod, or get too close to the cat until you first replace the goggles!

You should wear exam gloves (if you have a latex allergy, we do have nitrile gloves, and a few vinyl gloves for people who are also allergic to nitrile, available) when handling the cats, and thoroughly wash your hands after removing the gloves. It is suggested that you keep your gloves on while you put the cat away and wash the table and any equipment used. When everything else is done, then remove your gloves and wash your hands. Obviously, if a glove gets a hole in it, it should be replaced, but please do not “waste” gloves by constantly removing them just to draw a picture or something, then tossing them and getting a new pair. If you do need to temporarily remove a glove, if at all possible, please carefully remove it so that you can put it back on. Please, as much as possible, attempt to limit your glove consumption to one pair per lab period.

Cat parts should not be disposed of in the regular trash. Since we are “borrowing” cats from the A&P students, all cat parts should be returned to the bags with the cats, but in the unlikely event something should need to be thrown away, there is a special red, biohazard bag in a special red, biohazard “trash” can, into which that should be placed.

While there is no prohibition against doing so, there is no need to “disinfect” the tabletops after working on the cats! The point of all the preservatives in the cats is to be so toxic that they totally prevent the growth of any bacteria. Thus, any liquid left on the table after working on a cat is not “cat juice,” but rather is excess of those (toxic) preservatives. However... you do need to thoroughly wash the tables with warm, soapy water to remove all the preservative as well as any cat “crumbs” and fur, and then rinse the tables and the sponge you used to remove all the soapy water. DO NOT LEAVE FUR AND “CRUMBS” OF TISSUE IN THE SINK! (Collect them and put them in the red, biohazard bag.) If you have sponged most of the water off the tabletop, it should dry fairly-quickly on its own without the need to use a paper towel, but if, for some reason, you do really need to use a paper towel to dry it, please DO NOT get a whole handful of paper towels. Rather, just use one (or two?).

Any dissecting tools (blunt probe) used should be washed with warm, soapy water, rinsed, thoroughly dried, and then returned to their proper storage location.

Pregnant women are encouraged to read the MSDS for the preservative used on the cats in order to decide what safety precautions they wish to take. That probably should include not working directly over the cat at close range where one would be likely to breath a lot of preservative fumes.

Materials Needed:

• goggles and exam gloves
• previously-dissected cats from the A&P class
• blunt probe
• possibly, optional books (in addition to your protocol book and this Web page?), to help identify internal organs

External Anatomy:

Stormy’s Inner Eyelid Many animals have a “third eyelid” which sweeps across the eye to clean it, or in some animals, can be closed to protect the eye in a dusty situation. In humans, all we have left of this is the pink “lump” in the inner corner of our eye.

Frodo Being Sleepy As you know, when we humans close our eyes, it is our upper eyelid that goes down. Interestingly, in chickens, their lower eyelid goes up.

Sally Looking Forward
Sally Looking Sideways

An animal that is potential prey for another animal has its eyes on the sides of its head and the eyes operate independently, giving the animal nearly 360° vision to better watch for danger. A predator has its eyes on the front of its face, giving it excellent binocular vision for depth perception and judging distance to prey. An interesting combination of these traits can be found in a chameleon (not an anole). Chameleons eat insects, so need binocular vision to capture dinner, but are also potentially dinner for someone else. They have their eyes on the sides of their heads, but the eyes stick out and can swivel around. Chameleons can use their eyes independently to watch for predators, yet when a potential meal hops into sight, can focus both eyes on the insect to judge the distance before flicking out a sticky tongue to catch it. Interestingly, because of the location and mobility of a chameleon’s eyes, it can rotate its eyes backwards, and have binocular vision behind its head! Chickens, also, have their eyes on the sides of their heads, and they work independently to watch for predators, but chickens use their binocular vision to focus on the food they’re about to pick up.

Internal Anatomy:

Examine the preserved and dissected cat, and locate the following features. Review with your lab partner the function of each feature as you locate it. In your lab notebook, make labeled illustrations of 1) neck and thorax, 2) abdomen, and 3) ventral view of the brain, indicating the location of the features listed below. Also, take notes on locations, functions, etc. of the various organs/systems that you examine. Take the time to think about how what you’re seeing compares with what you already know about your own body, and write down your thoughts. Note that while, here, the organs are sorted/discussed by system, your drawings should be of the body regions just mentioned, and should include all organs/systems located within that body region. The letters in the list of body parts correspond to the labels on the photos, included below the list. More information on tissues and body system can be found on the Tissues, Organs, and Systems page.

• Respiratory System
  1. nasal cavity: This warms, moistens, and filters the air. The sinuses are convoluted, narrow passageways.
  2. nasal and oral pharynx: (pharynx = throat). Note proper pronunciation: “fair-inks.”
  3. larynx: This is also known as the voice box. The epiglottis (epi = upon, over) covers the larynx. Note proper pronunciation: “lair-inks.” The cricoid cartilage is between the larynx and trachea.
  4. trachea: (trachea = windpipe) This has cartilaginous rings (similar to those in a shop-vac hose) to hold it open. (The esophagus is the muscular tube right behind and parallel to it.)
  5. bronchi: The bronchi (singular = bronchus) are the two main branches from the trachea to the lungs. These are located behind the heart. An inflammation of the bronchi is called “bronchitis.” (bronch = windpipe)
  6. lungs: Cats’ lungs have 3 lobes on each side, whereas humans’ lungs have 2 lobes on the left side and 3 on the right. This may relate to the fact that, while our heart is located in the center of our chest, it does “lean” a bit toward the left.
  7. pleura: The thoracic cavity is lined by pleural membranes (pleura = rib, the side), which is smooth and slippery. Parietal pleura lines the outside wall of the chest, while the visceral pleura coats the organs (pariet = a wall; viscer = the organs of the body cavity). An inflammation of the pleura is called pleurisy: the inflamed membranes don’t slide well, but rub against each other, so it hurts to breathe.
  8. diaphragm: In mammals (including cats and humans), this muscle layer divides the abdominal and thoracic cavities (dia = across, through; phragm = fence) and is used to pull air into the lungs.
     However, that is not true of all other vertebrates. For example, a frog opens its nostrils and expands the floor of its mouth to draw air into its mouth. Then it closes its nostrils and uses the floor of its mouth to push air into its lungs.
     Birds also do not have a diaphragm, so their liver and heart are almost touching. If their liver becomes enlarged for some reason, it can rub on the bird’s heart, a sound which a trained veterinarian can hear. Birds have a number of air sacs which branch off their lungs. Their chest muscles move their sternum (breast bone) outward, thereby pulling air into the lungs and air sacs, and thus, it is critically important that a pet bird not be restrained so tightly that its chest cavity is unable to expand. Unlike us, they exhale by contracting other muscles to put pressure on the air sacs to push the air out. The lungs, themselves, do not expand and contract like mammalian lungs. Because of these differences, it takes two breath cycles for air to move in, throughout, and back out of the respiratory system. (This complex process is explained in greater detail on a number of other people’s Web sites: do a Google search for “how do birds breathe.”)
  9. phrenic nerves: This is a pair of nerves that regulate the diaphragm (one on each side). These are white “strings,” the bottom ends of which attach to the diaphragm. They run from the diaphragm, along either side of the heart, to the neck, then come out where the neck meets skull. (phreni = diaphragm)
  More information on the respiratory system can be found on the Respiratory System page.
• Cardiovascular (Circulatory) System
  10. mediastinum: This is the area between lungs: it contains the heart and thymus
  11. heart: Fish have a two-chambered heart (one atrium and one ventricle) which pumps blood to both the body and the respiratory system (gills). Amphibians and most reptiles have a three-chambered heart (two atria and one ventricle), so their heart separately receives blood from the body and from the respiratory system, but the blood mixes in the ventricle and is pumped back out to both the body and the respiratory system. Crocodiles (which are reptiles), birds, and mammals have four-chambered hearts (two atria and two ventricles). However, the evolutionary history of the crocodilian heart differs from that of the avian and mammalian hearts. In a four-chambered heart, the right atrium receives blood from the body. That is sent to the right ventricle, which pumps it to the lungs. The blood is returned from the lungs to the left atrium, and from there it goes to the left ventricle. The muscular left ventricle sends the blood out to the body.
  12. pericardium: This is the membrane around the heart. It is slippery and lubricated so that the heart can move freely as it beats. (peri = around, cardio = heart)
  13. atria: (singular = atrium) Mammals have two: a right and left atrium or auricle (atrium = vestibule, entrance hall; auricle = little ear). These are the upper portions of the heart and receive blood back from either the body (right) or lungs (left).
  14. ventricles: These are the lower, muscular portions of the heart and receive blood from the corresponding atria. Birds and mammals have two ventricles, and the left one is especially muscular to send blood to whole body.
  15. superior vena cava: This delivers blood from the head and arms to the right atrium.
  16. inferior vena cava: This delivers blood from the lower body to the right atrium.
  17. pulmonary trunk: The pulmonary trunk (or pulmonary artery) carries deoxygenated blood to the pulmonary arteries (which go to the lungs). It comes from the right ventricle, out on top of heart, then divides and goes to the lungs. The pulmonary vein carries oxygenated blood back to the heart from the lungs. (Note: arteries/veins are defined/determined by the direction of blood flow [arteries rarr; away], not by O₂-content. The umbilical artery also carries deoxygenated blood away from the baby to the placenta, and the umbilical vein carries oxygenated blood from the placenta back into the baby’s body.)
  18. aorta: This looks yellowish because it is so muscular/elastic. The first, big portion that goes up and over is the aortic arch. (aorta = heaving)
  19. carotid arteries: These are among the first to branch off the aorta. They go up to the neck, pass by the larynx, and go up into the head. These are large, red (because filled with latex), and carry the majority of blood to the brain.
  20. descending aorta: This is the portion of the aorta which goes down behind the left lung, through the diaphragm, and into the abdomen.
  21. common iliac arteries (left and right): These branch off the descending aorta where it ends at the hip (ilium = the groin, flanks). These are red because they are filled with latex. Each branches into a group of femoral (deep, superficial, common) arteries.
  22. common iliac veins: These run parallel to the iliac arteries and are filled with blue latex. They join to form the bottom end of the inferior vena cava (which goes to the heart).
  More information on the circulatory system can be found on the Circulatory System page.
• Lymphatic System and Immune System
  23. lymphatic system: This contains yellow latex. Its job is to filter fluid to remove bacteria, etc. Especially noticeable to the outside of the digestive and circulatory systems is a big, yellow trunk up to the left subclavian vein.
  24. lymph nodes: These yellow (laytex-filled) nodes may be easily found in the mesenteries that support the intestines. Other, less-obvious lymph nodes are found throughout our bodies. Because of their filtering functions, along with the bacteria that they “trap” and remove, they are also noted for their ability to “trap” metastasizing cancer cells, which then may start to grow in the lymph node. Thus, a lymph-node biopsy is often performed to determine how far someone’s cancer might have spread.
  25. thymus: The thymus, which is located in the thorax, activates T-cells to kill foreign tissue. It is especially large and obvious in childhood, but smaller in adults.
  26. spleen: This is located on the left side of the abdomen, by the stomach. It is involved in recycling blood cells, and is “famous” for becoming enlarged if someone has mononucleosis.
  More information on the immune system can be found on the Immune System page.
• Endocrine System
  27. thyroid glands: These are small and located, up near the larynx. Humans have one, united one, but in the cat, they are separate and are located on either side of larynx. The hormones they make regulate metabolic rate. They absorb iodine and make thyroxine.
  28. adrenal glands: In the cat, they do not sit directly on the kidneys, but are more medial (closer to the center) and are yellowish. Adrenal glands are the source of adrenalin (ad = to, toward; renal = kidney) and a number of other hormones.
  Note that the pancreas, testes, and ovaries, all described below, also serve endocrine functions. More information on the endocrine system can be found on the Endocrine System page.
• Nervous System
  29. brain: This is surrounded by three membranes called meninges: the outer one is the dura mater (dura = hard; mater = mother). Below, the major parts of the brain are described.
  30. cerebrum: Most of the brain is comprised of these two hemispheres (hemi = half). These control thought, motion, speech, etc., and each hemisphere controls the opposite half of the body.
  31. cerebellum: This is located behind the cerebrum and is the center of skilled physical movement and pattern. Someone who has had a stroke in his/her cerebellum may be able to move, but not put a series of movements together in a meaningful, useful way: for example, may not be able to pick up a fork, then use that to pick up some food and transfer it to his/her mouth. (cerebell = brain; -um = structure, tissue, thing)
  32. medulla oblongata: This is the center of involuntary, life-sustaining functions such as breathing, heart rate, and vomiting. It is the inferior-most portion of the brain. (medull = marrow, pith)
  33. pons: This is a “bridge” helps to connect the right and left sides of the cerebellum. (pons = bridge)
  34. optic nerve: You will probably observe this as cut-off stumps which form an “X"” under the brain. The optic nerves cross, here, to the other side of the brain.
  35. olfactory tract: This anterior-most portion of the brain is involved in our sense of smell, and can link those smells to past events such that a given smell may instantly and vividly evoke recollection of memories.
  Note that the phrenic nerves, described above, also are part of the nervous system. In general, the larger an animal is, the larger and more complex its brain often is. However, there has been some interesting research done on birds’ brains, which while considerably smaller than those of an equivalent-sized mammal, are “wired” just differently-enough that they are more efficient, often making a bird “smarter” than an equivalently-sized mammal. More information on the nervous system can be found on the Nervous System page.
• Digestive System (and associated abdominal organs)
  36. salivary glands: There are several of these, located in the sides of the face near the jaw, and connected by ducts beside the tongue. Salivary amylase is the main enzyme in saliva.
  37. esophagus: The esophagus runs posterior to the trachea and penetrates the diaphragm to connect to the stomach.
  38. stomach: The stomach starts at (is attached to) the diaphragm, and is a J-shaped bag. The main enzyme it produces is pepsin, and its average pH is about 1 to 1.5.
  39. pyloric sphincter: This is a constriction/valve at the bottom of the stomach, between the stomach and the duodenum. (pylorus = a gate-keeper)
  40. greater omentum: Not a functional part of the digestive system, per se, but connected to it, this is a fat-filled “skin” which is attached to the stomach, and from there, lies ventrally over the intestines and other abdominal organs. It helps to insulate and protect the abdominal contents. (oment = fatty skin)
  41. liver: This is the major metabolic organ in the body. It makes bile for fat digestion (bile emulsifies fat), and that bile is stored in the gall bladder prior to being secreted into the small intestine.
  42. gall bladder: This is the dark (raisin-like) spot in the center of the liver (the human gall bladder is below/behind the liver). Its bile duct connects it to the duodenum.
  43. duodenum: This is the first curve of the small intestine. The inner surface is covered with villi (“fingers”) to increase its surface area for better absorption and which give it a velvety appearance. (villi = shaggy hair)
  44. pancreas: This is grayish-brownish, “diffuse” and not really obvious if you don’t know where to look for it. It is located in the folds of the mesenteries, near the duodenum. It secretes digestive enzymes into the duodenum. It also serves an endocrine function, secreting glucagon and insulin to regulate blood-sugar level.
  45. peritoneum: This is similar to the pleura mentioned above, with the difference that it is located in the abdomen (while pleura is located in the thorax). Visceral peritoneum covers the intestines, while parietal peritoneum lines the outer wall of the abdominal cavity.
  46. mesenteries: The mesenteries are all the transparent membranes connecting and holding in place the intestines. The pancreas and a number of lymph nodes are located within the mesenteries.
  47. ileocecal valve: This is the junction between the last part of small intestine and the colon. (ileum = twisted)
  48. colon: Cats have a colon and cecum, but cats do not have an appendix. The colon is also known as the large intestine, and is shaped like a question mark (“?”). The cecum is a dead-end region by the junction with the small intestine (cec = blind), and in humans, the appendix is attached to the “blind” end of the cecum. The rectum (rect = straight) is the end of colon where feces are stored until eliminated.
  More information on the digestive system can be found on the Digestive System page.
• Excretory (Urinary) System
  49. kidneys: Osmosis occurs in the kidneys. They are connected by the ureters to the bladder.
  50. renal arteries: These supply the kidneys with blood, bringing them both nourishment and excess water and nitrogenous wastes to filter.
  51. renal veins: The diameter of the renal veins is bigger than that of the renal arteries because the veins carry blood under lower pressure.
  52. ureters: These carry urine from the kidneys to the bladder.
  53. urinary bladder: This stores urine until it is voided.
  54. urethra: This carries urine from the bladder to the outside. In males, the vas deferens connects with and empties into the urethra, so that both semen and urine can be voided via the penis.
  More information on the excretory system can be found on the Excretory System page.
• Reproductive System
  55. ovaries: These are present in females and produce eggs.
  56. fallopian tubes: These are present in females and transport eggs to the uterus. In birds, the fallopian tube has the extra functions of adding the egg white and shell around the egg/embryo. Note that, as in humans, to turn into a chick, the egg must first be fertilized by sperm which have traveled up to the vacinity of the ovary.
  57. uterus: This is present in females and is where embryos develop into babies. In humans, most females have one, central uterus in which (in most cases) one baby at a time develops. In cats, the uterus is “V”-shaped, allowing for numerous embryos to simultaneously attach at different points, resulting in a litter of kittens born at the same time. In birds, reptiles, etc., the zygote/embryo (AKA “fertilized egg”) is packaged into an egg shell, released from the female’s body, and develops externally. We placental mammals whose young develop within the mother’s uterus are the exception rather than the rule.
  58. vas deferens: This is present in males and joins the urethra to pass semen to the penis (in animals whose males have that organ — birds, for example, do not).
  59. testes: These are present in males and make sperm. They develop in the abdomen, in about the same location as ovaries do in females, then during embryonic deveopment, move downward and pass through the inguinal canal (just under the skin) and out into the scrotum. This is important because a) undescended testes are more prone to developing cancer and b) the sperm they produce need a slightly cooler environment than internal body temperature.
  60. testicular/ovarian arteries: These are the blood supply for the testes or ovaries. The testicular or ovarian arteries originate above/near kidneys (during embryonic development). In males, as the tested descend, their arteries grow longer, grow down with the testes.
  61. testicular/ovarian veins: These return blood from the testes or ovaries. Again, in males, thes elongate and grow down with the testes.
  Birds and some other vertebrates have a cloaca. This is an organ, a space, into which the colon, the urethra, and the oviduct(s) or vas deferens all open, and from which they all share a common opening to the outside. More information on the reproductive system can be found on the Reproductive System page and the Reproductive Physiology page.
• Skeletal System Key: S = shoulder, E = elbow, W = wrist,
  C = carpals (hand), D = digits (fingers), H = hip,
  K = knee, A = ankle (heel), F = foot, T = toes
  
  Amphibian (treefrog)
  
  Reptile (Green Anole) — © E. A. Stein
  
  Bird (Chicken)
  
  Bird (Chicken)
  
  Mammal (squirrel)
  
  Mammal (Horse)
  
  62. skeleton: Due to the way these cats have been dissected, you probably won’t be able to see any actual bones (maybe some ribs?). One important point to make, here, is that the skeletal structure of amphibians, reptiles, birds, and mammals is pretty-much the same. They all have the same bones in the same places, facing the same direction, as we humans do. Many people make the mistake of looking at the heel of a dog or goat or chicken, and think it is a “backwards” knee: it is NOT — it’s a heel! They are walking on tip-toe, their feet are a lot longer than ours, and their tibia (shin bone) is shorter. Their wrists, elbows, heels, knees, etc. are in the same positions and facing the same directions as ours.
  More information on the skeletal system can be found on the Skeletal System page.
  
• Muscular System
  More information on the muscular system can be found on the Muscular System page.

Cat Internal Anatomy — Thorax
Labels correspond to those of parts listed, above.
Cat Internal Anatomy — Abdomen

Clean-Up:

IMPORTANT: When you are finished, return the organs to their correct positions, close the peritoneal cavity, and wrap the skin closely around the cat. Slide the cat, head first and belly down, into its plastic bag. Press the air out, fold the bag over lengthwise, and secure the end with three turns of a sturdy rubber band. Return the bagged cat to the storage bag in the box. All cats should be headed the same direction in the box (all rubberbands on the same end of the box).

Clean up stray pieces and fur. As mentioned above, wash the desk top with soap and water, then rinse. Make sure any stray fur or “cat crumbs” are placed into the red bag. MAKE SURE TO CHECK THE DRAIN IN THE SINK YOU USED!

Other Things to Include in Your Notebook

Make sure you have all of the following in your lab notebook:

• all handout pages (in separate protocol book)
• all notes you take as you read through the Web page and/or during the introductory mini-lecture
• all notes and data you gather as you perform the lab
• labeled drawings (yours!) of
  • ventral view of neck and thorax area
  • ventral view of abdominal area
  • ventral (and side) view(s) of brain
• answers to all discussion questions, a summary/conclusion in your own words, and any suggestions you may have
• any returned, graded pop quiz