312 VERTEBRATE ZOOLOGY 



callosum. Now cut through the corpus callosum into the ventricle 

 and carefully chip away the entire roof of the latter, but do not 

 remove the fornix. The cavity is thus fully exposed. A prominent 

 ridgelike elevation of the floor of its anterior portion projects into 

 it ; this is the corpus striatum. A larger elevation of the floor of the 

 posterior portion is the hippocampus; along the entire anterior 

 border of the hippocampus is a vascular tract called the fimbria. 



Exercise 34. Draw a sketch showing these structures. 



The Spinal Cord. Remove the skin and muscles from the verte- 

 brae of the neck and trunk. With bone forceps remove the roof of 

 the neural arches of all the vertebrae and expose the spinal cord. 

 Note the tough membrane, the dura mater, which loosely envelops 

 the cord, and remove it. Closely investing the cord is a delicate 

 membrane, the pia mater, and between it and the dura mater a 

 third membrane, the arachnoid. Observe the spinal nerves issuing 

 from the intervertebral foramina, and their dorsal and ventral 

 roots. Observe the ganglion in the dorsal root, and also the two 

 rami of each spinal nerve. Posteriorly the cord diminishes in size 

 until it becomes a small strand called the filum terminale. Note 

 the enlargement of the cord in the cervical and lumbar regions. 

 In the sacral and caudal regions the spinal nerves are small and 

 directed backward. On both the dorsal and ventral surfaces of 

 the cord a median longitudinal fissure is present. 



Exercise 35. Draw an outline of the dorsal surface of the cord. 



Make a cross section of the cord and note the inner gray and 

 the outer white matter, the small central canal, and the dorsal 

 and ventral fissures. 



Exercise 36. Draw the cross section. 



The Muscular System. The superficial muscles alone will be 

 studied. Kill a rabbit and skin it. The cutaneous muscles which 

 produce movements of the skin will probably be removed with it. 

 These muscles are two in number, the great cutaneous and the 

 platysma. The former is a broad, thin, transparent muscle which 



