no VERTEBRATE ZOOLOGY 



by the infundibulum. Arising from the crura near the middle line 

 may be seen the very delicate oculomotor nerves. 



The medulla oblongata is but slightly wider than the spinal cord. 

 A longitudinal groove is present in the midventral line of both. 

 Exercise 15. Draw the ventral aspect of the brain on a scale of 3. 



The Ventricles of the Brain. With a sharp scalpel remove the 

 dorsal wall of the brain and expose the cavities within. Each 

 hemisphere has a large cavity ; these are called the first and second, 

 or lateral, ventricles. A median canal called the foramen of Monro 

 joins them with each other and with the third ventricle, which is 

 a narrow median space situated in the diencephalon. Extending 

 back from the third ventricle through the midbrain is a median 

 canal called the aqueductus Sylvii ; the large cavity in each optic 

 lobe is joined with it. The fourth ventricle is in the medulla ; it is 

 a triangular space which at its hinder end is continuous with the 

 central canal of the spinal cord. 

 Exercise 16. Draw a diagram showing these structures. 



The Vascular System. This system is made up of the following 

 parts : ( 1 ) the heart, a muscular pump which is continually driving 

 the blood to all parts of the body; (2) the arteries, the vessels 

 through which the blood is carried away from the heart; (3) the 

 veins, the vessels through which the blood is returned to the heart ; 

 (4) the capillaries, the minute vessels which connect the veins and 

 arteries. 



Kill a frog (as directed on page 93) and pin it down. Make a 

 midventral incision through the skin from the tip of the snout 

 to the anus. Note the prominent cutaneous veins on the inner 

 surface of the skin. Identify first the abdominal vein through the 

 ventral wall of the abdomen. This vein lies in the body cavity 

 against the ventral abdominal wall and will appear as a dark 

 median line. Open the body cavity— by a longitudinal incision 

 to one side of the midventral line, in order to avoid cutting the 

 abdominal vein— from the anus to the tip of the lower jaw. Take 

 great care not to cut the blood vessels or other organs within. 



Dissect the abdominal vein free from the body wall, or, if this is 

 difficult on account of the small size of the frog, slit the body wall 



