THE RABBIT 299 



Thirty-one pairs of spinal nerves are present (not counting 

 those in the tail) of which eight are cervical, twelve thoracic, 

 seven lumbar, and four sacral. These nerves pass from the 

 neural canal through openings between the vertebrae called the 

 intervertebral foramina. Each nerve arises from the spinal cord 

 by two roots which join immediately outside the intervertebral 

 foramen. Of these roots the dorsal one bears a ganglion and is 

 sensory in function, whereas the ventral root is motor. Immedi- 

 ately after its formation by the meeting of these roots, the spinal 

 nerve divides into two branches,— a smaller, dorsal and a larger, 

 ventral ramus. 



The sympathetic system consists of two rows of small ganglia 

 which lie one on each side of the spinal column against the 

 dorsal wall of the body cavity and in the neck, those of each row 

 being connected with one another by a slender longitudinal nerve 

 and with each spinal nerve by a short branch ; they are also joined 

 with various organs of the thoracic and abdominal cavities by 

 numerous nerves. The sympathetic system falls thus into three 

 divisions, the cervical, thoracic, and abdominal, the last two divi- 

 sions lying in the thoracic and abdominal cavities and being easily 

 seen lying against the dorsal wall, when not concealed by fat. 



Look for the longitudinal sympathetic nerves,— first in the tho- 

 racic cavity, where they lie along the vertebral column. Fol- 

 low them into the abdominal region, where they lie between the 

 abdominal aorta and the body wall. 



In the cervical region the longitudinal sympathetic nerve is so 

 closely joined with the vagus nerve that they appear like a single 

 strand ; this lies alongside the trachea, together with the carotid 

 artery and the internal jugular vein. A short distance in front 

 of the first rib they separate from each other, and the sympathetic, 

 which is the smaller of the two, passes into the thorax, and just 

 anterior to the subclavian artery enters the inferior cervical gan- 

 glion. Just posterior to this artery lies another ganglion, the first 

 thoracic ganglion, which is joined with the inferior cervical by two 

 nerves, one of which passes on each side of the artery. The cervi- 

 cal portion of the sympathetic nerve may be traced anteriorly to 

 the superior cervical ganglion, which lies at the base of the skull 



