394 hIERyOUS SYSTEM. 



small and supply the muscles and integument of the back. 

 Each gives off a branch directly dorsad to the spinal muscles, 

 and a lateral branch which reaches the integument some dis- 

 tance from the middle line. 



Ventral Rami. — The ventral ramus of the first thoracic 

 nerve enters into the brachial plexus, as already described. 

 The ventral rami of the other thoracic nerves form the inter- 

 costal nerves. Each of these passes ventrolaterad, lying close 

 to the caudal border of a rib, in company with the intercostal 

 artery. Branches are given to the intercostal muscles, and at 

 about the middle of the length of the rib a large lateral branch 

 is given off, which passes to the more superficial muscles of the 

 thoracic wall (serrati posteriores, obliquus externus, etc.), its 

 main branches running dorsad and ventrad. The main inter- 

 costal nerve extends ventrad to the transversus costarum and 

 rectus abdominis, supplying these muscles. 



C. Lumbar Nerves.— There are seven lumbar nerves, 

 one passing from the vertebral canal caudad of each lumbar 

 vertebra. 



Dorsal Rami. — The dorsal rami are similar to those of the 

 thoracic region, sending one branch dorsad to the muscles of 

 the vertebral column, another dorsolaterad to reach the integu- 

 ment at about the lateral border of the longissimus dorsi. The 

 dorsal rami are somewhat smaller caudad. 



Ventral Rami. — The last four lumbar nerves are intercon- 

 nected to form the lumbar or lumbosacral plexus. The first 

 three are distinct, and will therefore be described separately. 



The first three lumbar nerves are directed strongly caudad 

 (as well as ventrad), so that on leaving the intervertebral fora- 

 men they pass ventrad of the transverse process of the vertebra 

 immediately succeeding. Each communicates with the sym- 

 pathetic system and gives off near its origin branches to the 

 muscles on the ventral side of the vertebrae, — the first to the 

 crus of the diaphragm, the second and third (Fig. 162, //and 

 ///) to the quadratus lumborum and psoas muscles. Each 

 divides three to five centimeters from its origin into a lateral 

 and a medial branch, the first having a more cranial, the latter 

 a more caudal course. The first three nerves of the cat are 



