68 DISSECTION OF THE CAT 



canal of the spinal column. It is composed, as is 

 the medulla, of an inner core of gray matter and 

 of external columns of white fibres. A median 

 longitudinal fissure extends along both the mid- 

 dorsal and mid-ventral lines. In the brachial and 

 lumbar regions the cord becomes somewhat broad- 

 ened, to form the cervical and lumbar enlarge- 

 ments. In the sacral region the cord ends in a 

 small nerve-filament, the filum- terminale. The 

 filum terminale, together with the sacral nerves, 

 which lie parallel with each other for some dis- 

 tance in the vertebral canal, form the cauda equina. 



SPINAL NERVES. 



The Spinal Nerves each arise from the spinal cord 

 by a dorsal and ventral root, and pass out from the 

 neural canal through an intervertebral foramen. 

 The dorsal root bears a ganglion. After emerg- 

 ing from the neural canal, each nerve divides into 

 a dorsal and ventral branch. 



A— Brachial Plexus. (Plate VII., d.) 



The Brachial Plexus is the net-like arrangement 

 formed by the union of the ventral divisions of 

 the sixth, seventh, and eighth cervical and first tho- 

 racic nerves. Its branches supply the region of 

 the shoulder and arm. The principal nerves aris- 

 ing from the brachial plexus are : 



I. A small nerve, which supplies the rhom- 

 boideus muscle. 



