THORAX AND ABDOMEN OF THE HORSE 155 



from beneath the lateral border of the former muscle, and as it lies on 

 the transverse muscle of the abdomen, the nerve divides into two 

 branches. The superficial branch (ramus superficialis) pierces the 

 transverse muscle almost at once, and has already been found in the 

 abdominal wall. The deep branch (ramus profundus) runs ventralwards 

 and towards the pelvis between the peritoneum and the transverse 

 muscle, giving branches to the internal oblique and straight muscles of 

 the abdomen. 



N. ILIOINGUINALIS. — The ilio-inguinal nerve is derived from the 

 second lumbar nerve. Like the preceding, it lies at first between the 

 psoas major and quadratus lumborum, and also like the ilio-hypogastric, 

 divides into superficial and deep branches. The superficial branch 

 pierces the abdominal wall a short distance in front of the coxal tuber, 

 and is distributed over the front of the thigh and the lateral aspect of 

 the patellar region. The deep branch has a course and distribu- 

 tion similar to the corresponding branch of the ilio-hypogastric 

 nerve. 



The possibility that the ilio-inguinal nerve may end in branches dis- 

 tributed in the psoas major muscle must be kept in mind. 



N. GENITOFEMORALIS. — Though mainly formed by the ventral 

 branch of the third lumbar, the genito-femoral nerve generally receives 

 small contributions from the second and fourth nerves. After piercing 

 the psoas minor, the nerve runs towards the pelvis between this muscle 

 and the peritoneum, crosses the deep circumflex iliac vessels obliquely 

 (caudal, lateral and ventral), and divides into two branches. One of 

 these ends in the internal oblique and cremaster muscles. The other 

 (n. spermaticus externus) descends the inguinal canal, medial to the 

 constituents of the spermatic cord and in relation to the internal 

 pudendal artery, and ends in the external genitalia and the skin of the 

 inguinal region. This branch is not infrequently joined by one from 

 the ilio-inguinal nerve. 



N. CUTANEUS FEMORis LATERALIS. — The lateral cutaneous nerve 

 of the thigh arises by two roots from the third and fourth (often also 

 the fifth) lumbar nerves. The first part of its course is between the 

 psoas minor and major muscles. Appearing at the lateral margin of 

 the former, it crosses the surface of the latter muscle, where it comes 

 into relation with the deep circumflex iliac vessels, the caudal branch 

 of which it follows. Thus the terminal part of the nerve pierces the 

 abdominal wall close to the coxal tuber of the ilium to be distributed 

 over the patellar region. 



