324 The Nerves and Muscles of the Leg 
embryo. The two muscles are clearly differentiated from one another, 
but the gluteus medius is partly fused to the piriformis and in this em- 
bryo the piriformis has not extended to the sacrum. In other embryos 
of about this stage the piriformis has, however, become attached to the 
sacrum. he distribution of nerves to these muscles is very similar to 
that found in the adult. The tensor fasciz late extends distally over the 
thigh into the anlage of the tractus ilio-tibialis which at this period is 
but slightly marked. 
In subsequent development the iliac ala imcreases in size and the 
muscles extend over it to their adult attachments. With the develop- 
ment of the anterior superior spine of the ilium the iliac attachment of 
the tensor fascizw late is carried far from its original position near the 
back of the head of the femur. 
2. Individual Muscles. 
Tensor fascie late.—This is differentiated near the lateral edge of the 
anlage of the gluteus medius and minimus. According to Grafenberg, 
04, it is at first closely fused with this anlage and extends from the 
“ Beckenschaufel” to the anlage of the great trochanter. In the speci- 
mens which I have studied the anlage of the muscle when it first becomes 
distinct has no skeletal attachment but lies near the gluteal anlage (Plate 
VIII, Fig. 4). From here it shifts laterally and its proximal extremity 
soon becomes attached to the ilium somewhat distal to the crest and be- 
hind the anlage of the anterior superior ihac spine. Distally it extends 
toward the lateral] side of the knee (Plate VIII, Fig. 5) and is continued 
into the tractus iliotibialis which toward the end of the second month 
begins to be distinct. 
In the adult the nerve usually enters the muscle about midway between 
its origin and insertion. This area corresponds to that first differentiated 
in the embryo. 
It seems probable that that portion of the m. ilio-tibialis of urodeles and 
reptiles innervated by the sciatic nerve (the m. gluteo-rectus) represents the 
tensor fascia late of mammals. In different mammals the tensor fascie# 
late varies greatly in development. It is said not to be present in mono- 
tremes and marsupials (W. Leche). It is large in all anthropoids except 
the orang (Le Double). 
Gluteus medius and minimus.—These two muscles are differentiated 
in close association with one another and remain closely associated in the 
adult. The myoblastema from which they are derived lies close to the 
back of the embryonic skeleton near the junction of the femur with the 
pelvis (Plate VIII, Fig. 4). The anlage of the two muscles seems from 
