114 ANATOMY OF THE RAT 



tor foramen of the coxal bone to the adjacent muscles. The 

 sciatic nerve may be traced from the lumbar plexus to the 

 deeper posterior muscles of the thigh. 



The remainder of the fifth lumbar nerve, and the sixth 

 lumbar nerve, together with part of the first and second 

 sacral nerves, form the sacral plexus. There are four 

 pairs of sacral nerves. Locate the caudal nerve in the 

 tail and trace it forward to its connections with the sacral 

 nerves. 



Exercise XXX. Sketch the spinal and sympathetic nerves of 

 one side of the body. 



THE SPINAL CORD (SPINAL MEDULLA) 



Clear away the muscles surrounding the backbone and 

 sever the head from the body at the articulations between 

 the cranium and the atlas. Carefully expose the spinal 

 cord throughout its length by removing the roof of each 

 neural arch. The cord is surrounded by tough membranes, 

 the meninges. 



Observe the connections of several of the spinal nerves 

 with the cord. Each nerve proceeds from the cord as a 

 pair of roots, a dorsal and ventral. The former bears a 

 swelling, or ganglion. Trace a pair of roots from their 

 origin to the point where they unite to form the spinal 

 nerve. The dorsal ganglia in mammals contain the cell 

 bodies of sensory neurons which send some of their fibers 

 through the dorsal root to the spinal cord, and other fibers 

 distally to the spinal nerve. The dorsal root is, therefore, 

 sensory in function. The ventral root carries motor fibers 

 from nerve cells located in the cord itself. Thus each spinal 

 nerve carries nervous impulses both to and from the spinal 

 cord. 



Observe the cervical and lumbar enlargements of the 

 cord in the neck and lumbar regions, respectively. The 



