THE PERIPHERAL NERVOUS SYSTEM. 395 



represented in man by the iliohypogastric and the ihoinguinal 

 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, a) 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 pas.ses, 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 {b) 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 



