DISSECTION OF THE DOG 75 



psoas minor and ilio-psoas muscles the lateral cutaneous femoral nerve 

 makes its exit from the sublumbar muscular mass. A small nerve, the 

 genito-femoral, runs obliquely across the surface of the psoas minor 

 muscle ; and along the medial border of the same muscle the lumbar 

 part of the ganglionated cord of the sympathetic nerve should be found. 

 After the foregoing nerves have been recognised, they should be followed 

 to their several origins. This must be done by removing the psoas minor 

 and psoas major muscles piecemeal. 



N. ilio-hypogastrictts. — The ilio-hypogastric nerve, the ventral branch 

 of the first lumbar spinal nerve, pierces the quadratus lumborum muscle and, 

 accompanying the phrenico-abdominal vessels, crosses the aponeurotic origin 

 of the transverse abdominal muscle to dip into the fleshy part where it divides 

 into two branches. 



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

 lumbar nerve. After having pierced the quadratus lumborum muscle, it has a 

 course similar to that of the preceding. 



N. genito-femoralis. — The origin of the genito-femoral nerve is irregular. 

 Generally it arises by two roots from the third and fourth lumbar nerves, and, 

 running almost directly towards the pelvis, comes into contact with the external 

 iliac artery. Following the external pudendal vessels, its termination, as the 

 external spermatic nerve, is in the skin of the penis, scrotum, and medial aspect 

 of the thigh. 



N. ctttanetjs femoeis lateealis. — The lateral cutaneous femoral nerve 

 may arise by one or two roots from the third and fourth lumbar nerves. It 

 either pierces the psoas minor muscle, or appears between the two psoas muscles. 

 Crossing the psoas major and quadratus lumborum the nerve perforates the 

 transverse muscle of the abdomen in company with the circumflex iliac 

 vessels. 



N. femoralis. — The femoral nerve is larger than the foregoing, and is 

 formed mainly by roots from the fourth and fifth lumbar nerves. The third 

 nerve, however, assists. The femoral nerve passes through the psoas major 

 muscle, to which it supplies branches, and ends, as will be seen later, in the 

 muscles in front of the thigh. 



Dissection. — Follow the external iliac artery into the thigh. Examine the 

 fat-laden fascia of the inner side of the thigh and note its continuity with 

 the fascia of the abdomen. 



A. tliaca externa. — The external iliac artery leaves the aorta on a level 

 with the sixth lumbar vertebra. It runs obliquely across the tendon of the 

 psoas minor and the ilio-psoas muscles, and ends on a level with the brim of the 

 pelvis by becoming the femoral artery. 



