THE PERIPHERAL NERVOUS SYSTEM. 395 
represented in man by the iliohypogastric and the ilioinguinal 
nerves. There seems no good ground for applying these 
names to two of the three in the cat, in preference to the third, 
so that we shall speak of these nerves in the cat as simply the 
first, second, and third lumbar nerves. 
1. The first lumbar nerve arises from the intervertebral fora- 
men caudad of the first lumbar vertebra. Its lateral division 
passes between the transversus and obliquus internus muscles, 
then between the obliquus internus and externus. At about 
the middle of the abdomen it pierces the obliquus externus and 
is distributed to the integument of the middle of the ventral 
surface of the abdomen. The medial division passes between 
the obliquus internus and transversus, crosses the lateral divi- 
sion of the second (lying mediad of it), and extends to the. 
rectus abdominis, which it supplies. 
2. The second lumbar nerve (Fig. 162, 2) divides, like the 
others, into two branches. The lateral branch pierces the 
muscles of the abdominal wall at the lateral border of the 
longissimus dorsi and passes, lying just beneath the integu- 
ment, ventrocaudad nearly to the pubis. It supplies the 
integument of the caudal half of the abdomen and of the fold 
between the thigh and abdomen. The medial branch passes 
at first almost directly caudad, lying on the medial surface of 
the transversus abdominis; it curves gradually ventrad, lying 
in the substance of the transversus, and reaches the rectus 
abdominis three or four centimeters craniad of the pubis. 
3. The third lumbar nerve (6) is not united with the fourth, 
as in many animals, but remains distinct. It divides one or 
two centimeters from its origin. ‘The lateral branch passes 
caudad to the outer surface of the abdominal muscles, and 
extends, lying just beneath the integument, to that portion of 
the abdominal wall which is partly covered by the thigh. The 
medial branch passes caudad on the lateral surface of the 
iliopsoas muscle, follows the iliolumbar artery for a short dis- 
tance, and gives branches to the caudal part of the transversus 
and rectus abdominis muscles. 
The Lumbar Plexus (Fig. 162).—The fourth, fifth, sixth, 
and seventh lumbar nerves are interconnected by short 
