THE CAT 241 



The lateral cutaneous nerve arises principally from the fifth 

 lumbar nerve and passes through the abdominal wall to the 

 posterior side of the thigh. 



Study the three sacral nerves. The first sacral is the hinder- 

 most of the two large nerves that form the main roots of the 

 great sciatic nerve. 



Exercise 32, Draw a diagram of the lumbosacral plexus and the 

 nerves which issue from it, so far as observed. 



The dorsal rami of the caudal spinal nerves supply the dorsal 

 side of the tail ; the ventral rami are connected with one another 

 and with the last sacral nerve by a longitudinal nerve. 



The sympathetic system consists of two rows of small ganglia, 

 which lie 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 longitudinal nerve, and with the 

 spinal nerves by short branch nerves; they are also connected 

 with various organs of the thoracic and abdominal cavities, by 

 numerous nerves which in certain places form plexuses. 



The sympathetic system falls into three divisions : the cervical, 

 thoracic, and abdominal. The thoracic and abdominal divisions,, 

 which lie in the cavities of the same names, are easily studied. The 

 two longitudinal nerves will here be seen lying against the dorsal 

 body wall on each side of the spinal column. In the abdominal 

 cavity they lie nearer together than in the thoracic, gradually be- 

 coming smaller toward the posterior end of the abdominal cavity, 

 where they finally come to an end. In both these cavities a pair 

 of sympathetic ganglia is present opposite each vertebra, and a 

 short connecting nerve joins each ganglion with a spinal nerve. 



Look for the longitudinal sympathetic nerves, first in the ab- 

 dominal cavity, where they lie against the vertebrae. Note the 

 sympathetic ganglia here and follow the connecting nerves which 

 join them with the corresponding spinal nerves. Follow then the 

 longitudinal nerves into the thoracic region. 



In the cervical region the longitudinal sympathetic nerve is so 

 closely joined with the vagus that the two appear like a single 

 strand ; this lies along the trachea together with the carotid artery 



