304 The Nerves and Muscles of the Leg 
anlage. The first well marked differentiation of the sartorius anlage 
takes place in a region corresponding with that in which the nerves enter 
the muscle in the adult, Plate VI, Fig. 1. From here the differentia- 
tion of the muscle extends towards its iliac and tibial attachments. The 
embryonic muscle is proportionately larger than the adult muscle and 
forms more extensive tibial attachment. (Plate VI, Fig. 2, Plate VIII, 
Big. 2). 
Simultaneously with the differentiation of the muscle, branches extend 
into it from the femoral nerve. These branches are more or less inti- 
mately bound up with the anterior (middle) cutaneous nerve. As a rule 
there are two main branches, one of which serves to supply chiefly the 
lateral and proximal, the other the distal and medial, portion of the 
muscle. For the distribution of branches in the adult, see Frohse, 98. 
In the urodeles the sartorius does not seem to be represented. In reptiles 
it is probably represented by the ambiens or the pubi-tibialis or both. The 
ambiens arises either from the ilium, as in the crocodile, or from the pubis, as 
in most forms. Its tendon passes to the front of the leg. It is an extensor 
of the knee. The tendon of the pubi-tibialis passes to the back of the leg. 
It is a flexor of the knee (Gadow, 82). It is probably not homologous with 
the pubi-tibialis of urodeles, which is innervated by the sciatic nerve and is 
a differentiated portion of the pubi-ischio-tibialis. 
In the monotremes and insectivora the proximal attachment of the sartorius 
is in the neighborhood of the ilio-pectineal eminence. In the marsupials, 
prosimians, and primates it takes place into the ventral margin of the ilium. 
In other mammals it may take place in either place or from an intermediate 
region, from the ilio-pectineal fascia, the tendon of the psoas minor, the in- 
guinal ligament, etc. (W. Leche). The insertion takes place into the medial 
side of the tibia or into the crural fascia. It may be fused with the gracilis 
at its insertion. It may be double (dog—Ellenberger and Baum). The 
partial longitudinal splitting of the muscle found in the dog and other carniv- 
ora and as a variation in man may possibly indicate a primitive relation- 
ship to two muscles, the ambiens and the pubi-tibialis of reptiles. There 
seems to be nothing either in the phylogenetic or the ontogenetic history of 
the muscle to account for the transverse tendinous inscription or tendon 
which occasionally is found dividing the muscle into two parts. 
Quadriceps Femoris Muscle, Plate VI. Rectus Femoris.—This muscle 
is developed from the quadriceps muscle mass by gradual differentiation. 
Its tendon of attachment to the anterior inferior iliac spine is developed 
later than that to the supra-acetabular groove, Roger Williams, 78, and 
is a consequence of the development of the iliac blade, Le, Double, 97- 
As a rule the nerve to the muscle divides into two main branches, one 
of which goes chiefly to the medial half, the other chiefly to the lateral 
half of the muscle. The main trunk of the former, which enters about a 
