300 The Nerves and Muscles of the Leg 
C. DEVELOPMENT OF THE MUSCULATURE AND DEVELOP- 
MENT AND VARIATION IN DISTRIBUTION OF THE 
NERVES TO THE MUSCLES OF THE INFERIOR EX- 
TREMITY. . 
I. FEMORAL GROUP. 
a. Embryonic Development. 
1. General Features. 
Soon after the femoral nerve begins to extend into the base of the 
limb differentiation of the femoral musculature commences. At about 
the center of the shaft of the femur a mass of tissue may be distin- 
guished as the anlage of the quadriceps muscle (Plate III, Fig. 2). 
Into a cleft in this tissue the main trunk of the femoral nerve extends 
and gives off branches for each of the main divisions of the quadriceps. 
Anterior to this an ill defined mass of tissue may be distinguished as 
the anlage of the sartorius muscle. A special nerve is given to this. 
About the main trunk of the nerve as it passes over the region of the 
acetabulum a mass of tissue represents the anlage of the iliopsoas and 
possibly also the pectineus muscles. In this region the lateral and an- 
terior cutaneous nerves of the thigh pass toward the ectoderm. Distal- 
ward the anlage of the saphenous nerve may be seen. 
In a slightly older embryo (Plate VI, Fig. 1) the muscle differentia- 
tion is much further advanced. The sartorius muscle extends well 
toward the blastema of the ilium and toward the medial surface of the 
proximal end of the tibia. Definite tendons are not, however, developed. 
The nerve to the sartorius extends a short distance distally within the 
substance of the muscle. The ilopsoas muscle is likewise further differ- 
entiated and has extended more toward the vertebral column. The 
pectineus muscle has become distinct and to it runs a branch from the 
femoral nerve. 
The quadriceps muscle begins to show definite differentiation. Ten- 
dons of attachment are not, however, clearly differentiated. The vari- 
ous branches of the nerve to this muscle, Fig. a, have extended further 
into the body of the muscle. They follow in this course developing lines 
of cleavage of the muscle into its constituted portions. 
The various cutaneous nerves mentioned above have extended con- 
siderably in length and in addition there are two medial cutaneous 
branches. ‘These run toward the skin in the dense fascia which now 
separates the obturator from the femoral group of musculature. 
In an embryo of 20 mm. (Plate VI, Figs. 2 and b) the individual 
muscles of this group are clearly demarkated. .The figures illustrate 
