Charles R. Bardeen 267 
The obturator nerve arises from the first four lumbar nerves, passes 
through the obturator notch of the hip girdle and divides into two main 
divisions. Each of these terminates in a differentiated mass of tissue, 
the more anterior of which represents the adductor longus and brevis 
and the gracilis muscles, the more posterior, the obturator portion of the 
adductor magnus and possibly also the obturator externus muscle. 
The tibial nerve arises from the fourth and fifth lumbar and first 
three sacral nerves. From it branches pass to muscle masses represent- 
ing the obturator internus, quadratus femoris, hamstring, and the super- 
ficial and the deep posterior crural musculature. Distal to the tibial 
nerve the posterior cutaneous nerve of the thigh and the pudendal and 
caudal nerves may be seen. 
In Fig. E, Plate V of the article by Bardeen. and Lewis, o1, the 
urachus was represented much foreshortened in order to reveal the 
muscle masses of the leg. In Fig. 1, Plate III, the urachus is outlined 
in its true position as seen directly from the side. 
In Plate III, Fig. 2, the genital and lumbo-inguinal nerves are seen 
passing ventro-laterally from the junction of the 1st and 2d lumbar 
nerves. The femoral nerve is seen passing outwards over the region of 
the acetabulum. It is surrounded laterally by the ihopsoas muscle mass 
and terminates in the quadriceps femoris muscle mass. From it arise 
lateral and anterior cutaneous branches, a branch which passes to the 
sartorius muscle mass, and the saphenous nerve. 
The peroneal nerve arises from the 4th and 5th lumbar and first two 
sacral nerves, gives off branches for the anlages cf the superior gluteal, 
inferior gluteal, short head of the biceps and peroneal muscle masses and | 
terminates in the anterior crural muscle mass. 
An idea of the relations of the main nerves as they enter the limb in 
Embryo CIX may likewise be gained from Plate III, Fig. 3. The pelvis, 
the abdominal and dorsal musculature, the lining of the body cavity, the 
border nerves and the main nerve trunks of the limb are here represented 
as viewed from in front. The femur and the main nerve trunks are 
shown cut in a plane somewhat distal to the head of the femur. The 
division of the main nerve trunks into separate branches for individual 
muscles is schematic. 
III. MUSCLE DIFFERENTIATION. 
At the period under consideration several possibilities of muscle differ- 
entiation must be considered. ist——The tissue which represents the 
muscle masses just mentioned may extend into the limb-bud with the 
