Mammalia. 147 



Between the skull and the first vertebra is a space covered 

 by a thin membrane, through which the spinal cord may be seen. 

 Carefully cut through this membrane, and insert the point of one 

 blade of a pair of bone forceps at one side of the spinal cord. 

 Cut through this side of the arch of the vertebra ; repeat this on 

 the other side, and so on, through the whole length of the spinal 

 cplumn, removing the dorsal parts of the vertebrae, held together 

 in one strip by the connective tissue. The bony cavity in which 

 the spinal cord lies is the neural cavity. 



The work may be more easily done if the rabbit is supported 

 on the edge of a short piece of " two by four " scantling nailed 

 to a baseboard 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 labor. 



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 : (i) 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 



