32 SPINAL NERVES. 



short piece of " two by four " scantling nailed to a base-board 

 eight inches wide and a foot and a half long. 



Now look for the Spinal Nerves, which leave the spinal 

 cord in pairs, right and left, between the successive vertebrae. 

 It will probably be necessary to cut away considerably more 

 bone to expose the nerves. The whole of this work requires 

 the utmost care and patience, and involves a good deal of 

 hard muscular exertion. 



Note carefully the variations in the diameter of the spinal 

 cord in its course. The anterior swelling is called the Cervi- 

 cal Enlargement, and the posterior is the Lumbar Enlargement. 



When the spinal nerves have all been laid bare, count and 

 compare them in reference to : 



1. Size. 



2. Intervals between successive pairs. 



3. Angles at which they leave the spinal cord. 

 Carefully cut away the bone around some of the nerves in 



the region of the shoulder, and find the two Roots by which 

 each nerve is connected with the cord, one nearer the back, 

 the Dorsal Root, and one nearer the ventral surface of the body, 

 the Ventral Root. Trace these two roots, and note that they 

 unite and form a spinal nerve. 



On the dorsal root, just before it joins the ventral, is a 

 small swelling, the Ganglion of the dorsal root. 



In the region of the shoulder carefully trace several of the 

 nerves as they unite to form the Brachial Plexus, from which 

 nerves supply the fore limb. 



In the region of the hips trace several of the spinal nerves 

 to their union in the large Sciatic Nerve, which runs down the 

 thigh. 



Turn now to the head, and cut through the bone between 

 the eyes. Cautiously working backward, the whole of the 

 brain may be unroofed. Great care must be exercised, for 



