394 NERVOUS 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. 
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 dorsa 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 vertebrz,—the first to the 
crus of the diaphragm, the second and third (Fig. 162, // and 
ZIT) 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 
amore caudal course. The first three nerves of the cat are 
