A FROG 175 



At the anterior end of the kidneys is a pair of prominent, yel- 

 low, branching fat bodies. They vary much in size at different 

 times of the year, being largest before the breeding season and 

 smallest after it. 



While studying the urinogenital system, the organs of which it 

 is composed need not be disturbed. With a strong scalpel cut 

 through the bony pelvis exactly in the median line between the 

 legs in order to expose the cloaca. The urinary bladder is a del- 

 icate structure which is attached to the body wall by mesen- 

 teries. It must be freed from these and great care taken not 

 to cut either it or the cloaca. 



Exercise 9. Make a semidiagrammatic drawing of the urinogenital 

 system with the cloaca ; label carefully all its parts. 



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

 divisions : (i) the central nervous system, which is composed of 

 the brain and the spinal cord ; (2) the peripheral nervous system, 

 which is composed of {a) the paired cranial and spinal nerves and 

 (6) the sympathetic nervous system ; and (3) the special sense 

 organs. 



The cranial nerves and the spinal nerves each number ten 

 pairs ; the former spring from the brain and the latter from the 

 spinal cord and place these structures in communication with 

 the various organs and tissues of the body. The sympathetic 

 nervous system lies in the body cavity in connection with the 

 cranial and spinal nerves and innervates certain important viscera. 



Remove the urinogenital system from the body. Raise it care- 

 fully with forceps, and with fine scissors cut it loose from the 

 dorsal body wall. Note the spinal column projecting into the 

 body cavity, and lying ventral to it note a large blood vessel, 

 the dorsal aorta ; this must not be disturbed. The spinal column 

 is made up of nine vertebrae and a long terminal bone called the 

 urostyle. Identify them. 

 We shall study first the spinal nerves and the sympathetic sys- 

 tem. Each spinal nerve is joined with the spinal cord by two 

 roots, a dorsal and a ventral root, and passes out from the 

 neural canal of the spinal column through a space between two 



