72 VERTEBRATE ANATOMY 



Exercise XIV 



course, so don't linger with it here.) Next find 

 the trachea; look for the thyroid g\&nds clinging 

 to its side about two-thirds of the way to the 

 mouth. Free the trachea from the esophagus and 

 carefully dissect the bronchi and lungs free. 



Next look at the internal reproductive organs. 

 If your rat is a male, push the testis up into the 

 abdomen. Note the tubular epididymis attached 

 to the testis. Follow the ductus deferens to the 

 seminal vesicles. Slit open the epididymis and 

 squeeze some of its contents onto a microscope 

 slide. Add a drop of saline and cover with a 

 cover slip. Observe the sperm under the micro- 

 scope. If your preparation is reasonably 

 fresh, the sperm should still be motile. Describe 

 their motions. In the female, find the ovaries. 

 Follow Xht fallopian tubes to the uterus. 



Now turn to the muscular system. First skin 

 the animal. This can be done easily with blunt 

 dissection and the fingers. The pelt can be re- 

 moved in one piece. Dissect one foreleg and hind 

 leg. Identify as many muscles as you can. (The 

 best procedure here is to peel off the overlying 

 connective tissue, cut across the muscle or its 

 tendon at one end, and strip the whole muscle 

 back.) Note the large nerves entering the limbs; 

 these are seen best by excising the muscles on 

 the under side of the forelimbs or on the rear 

 of the hind limbs. 



Next cut through one side of the jaw. Look 

 at the tongue and remove it. Find the opening 

 of the esophagus. How do the teeth differ from 

 ours? How many different types of teeth do you 

 see? 



Rongeurs will be available for exposing the 

 brain. First remove the eyes, and then cut across 

 the skull between the eyes. Making small snips, 

 cut away the brain case overlying the brain. (Be 

 careful; the brain is very fragile!) When you 

 have exposed the brain, lift it from the anterior 

 end. Note the cranial nerves (especially the optic 

 nerves) on the underside. Free the brain, and 

 either remove it entirely or continue the dissec- 

 tion down the spinal cord. Note the nerves com- 

 ing from the spinal column. Note also the way 

 the cord bulges where the nerves to the fore limbs 

 come off. Where does the spinal cord terminate? 



If you continue to dissect down the spinal 

 cord, it may be helpful to turn the animal on its 

 back. Follow an arm or leg nerve out into a 

 limb. Eventually remove both cord and brain. 

 Cut the brain through longitudinally. Note the 

 grey and white matter (especially in the cere- 

 bellum). What do they represent? Cut across 

 the cerebral hemispheres, and note the tracts of 

 white matter. Cut other cross sections, and at- 

 tempt to follow some tracts. 



THE FROG 



Follow the directions given for the rat as far as 

 they are applicable. You should be able to find 

 almost all the organs mentioned in the rat dis- 

 section. On opening the abdomen, however, 

 note immediately that the frog has no diaphragm. 

 How does it breathe? 



Look at the beating heart under the dissecting 

 microscope. Follow the major vessels. Can you 

 see the blood flowing? Look at all the body con- 

 tents of the frog under the dissecting microscope. 

 When you find interesting things, show them to 

 your partner. 



Follow the dissection guide given for the rat. 

 (If you have a female frog, the abdominal con- 

 tents may be filled with two masses of dark 

 spherical bodies. These are the ovaries filled 

 with growing eggs. Remove them immediately 

 on beginning the abdominal dissection.) 



You will have an easier time dissecting the 

 visceral organs than your partner. You may 

 have trouble identifying the kidneys. They are 

 long, narrow organs found close to the midline 

 on the dorsal body wall. The adrenal glands 

 are the long yellow structures applied to the 

 kidney's surface. The testes are small white 

 bodies suspended from the kidney. Compare 

 your dissection with that of your partner and 

 note the differences in the two animals. 



The frog nerves and muscles will remain ex- 

 citable for most of the day. Stimulators will be 

 available (your instructor will demonstrate them 

 for you). Try stimulating various nerves and 

 muscles; learn their names, and show them to 

 your partner. 



