ANATOMY AND PHYSIOLOGY 17 



sels (Fig. 16). Be prepared to discuss the circulation of blood in 

 terms of what is carried to and from the different organs of the body. 



(f) Make a drawing (X 5) of the veins as dissected in your own 

 specimen. Spread the kidneys apart in the mid-line and show them 

 in outline. Pay especial attention to the representation of the origin 

 of the postcaval vein. The branches of the renal portal veins are to 

 be indicated by broken lines in the outline of the right kidney. Use 

 arrows to indicate the direction of blood flow. 



Exercise 15. — The Capillaries. 



(g) Examine a demonstration of the circulation of the blood 

 through the capillaries in the web of a frog's foot. How can you 

 distinguish arteries, capillaries, and veins? Notice the pulse. Why 

 does it occur? In what vessels is it seen? What is the relative size 

 of the blood cells, or corpuscles, and the smallest blood vessels? Can 

 you distinguish more than one kind of blood cell? Capillaries like 

 these are present in all the organs of the body of a vertebrate animal 

 (Fig. 17). What important relationships do capillaries have to 

 metabolism? Understand the relationship between the smallest lymph 

 vessels and the blood capillaries. 



F. The Respiratory System 

 Exercise 16. — The Lungs and Air Passages. 



(a) Remove the heart but do not injure the lungs. Carefully clean 

 off the area between the anterior ends of the lungs and find the semi- 

 transparent floor of the larynx with which the lungs are continuous. 



(b) Study the mouth cavity again. Observe the two internal 

 nares close to the vomerine teeth on the roof of the mouth cavity. 

 Pass a bristle through the nasal canal on one side. Find the glottis, 

 a vertical slit in a slightly raised area ventral to the esophagus on the 

 floor of the mouth cavity. The posterior forked end of the tongue 

 extends to the sides of the glottis in the living frog. Pass one end 

 of your forceps through the glottis and observe the tip through the 

 floor of the larynx. What is the course of air from the outside to the 

 lungs? Compare with man (Fig. 18). Notice the openings of the 

 Eustachian tubes on the roof of the mouth cavity near the angles of 

 the jaws. These tubes connect the mouth cavity and the cavities 

 of the middle ears (c/. Fig. 19). Understand their relationship to the 

 respiratory system of aquatic vertebrates. 



(c) Watch a living frog under a bell-jar. Time the respiratory 

 movements of the nostrils, the floor of the mouth cavity, and the sides 

 of the body. Understand the method of inhaling and exhaling air in 



