330 The Nerves and Muscles of the Leg 
quently has a tendon of insertion more or less distinct from that of the long 
head. Its tendon of origin may be attached to the tuber ischii, the fascia 
covering the gluteus maximus, or the sacrotuberosal ligament. 
a. Embryonic Development of Gluteus Maximus. 
The gluteus maximus arises from an anlage which lies dorso-lateral to 
the anlage of the great trochanter (Plate III, Fig. 2). Its proximal 
edge overlaps and lies near but does not seem to be fused with the gluteus 
medius anlage. Distally it is slightly fused with the anlage of the short 
head of the biceps. Into the gluteus maximus anlage two nerves extend 
from the back of the sacral plexus. 
In an embryo of 14 mm. (Plate II, Fig. 3; Plate VIII, Fig. 4) the 
gluteus maximus is quite distinct from the neighboring muscles.” It is 
beginning to show a division into two portions each of which is supplied 
by a separate nerve. The more distal of the two portions is continuous 
with the blastema of the femur. Proximally the muscle is extending over 
the gluteus medius and obturator internus anlages toward the ilium and 
sacrum. I find no primitive intrapelvic extension of the gluteus maximus 
such as that described by Grafenberg, but the fascial extension which he 
describes from the dorsal muscles over the gluteal muscles is quite evi- 
dent (see Plate II, Fig. 3). 
In an embryo 20 mm. long (Plate VIII, Fig. 5) the gluteus maximus 
has extended from the trochanteric region where it first appears to the 
ium, sacrum and coccyx. It is at this period very distinctly separated 
into two portions the more distal of which is inserted into the femur 
distal to the great trochanter while the more proximal is inserted into the 
fascia over the attachment of the distal portion. In the adult the two 
portions are only rarely thus distinct. The distal portion represents the 
femoro-coccygeus muscle so common in the-lower mammals. In the 
younger embryos two nerves pass from the plexus to the muscle. In this 
embryo a special nerve is given to each portion of the muscle, but the 
two nerves arise by a common trunk from the plexus. The nerve to the 
superficial portion of the muscle curves toward the ilium and passes up- 
wards on the deep surface of the muscle along a line about midway be- 
tween the origin and insertion of the muscle. The nerve to the distal 
portion passes distally and enters its proximal margin (Plate VIII, 
Fig. 5). 
& The early union with the piriformis described by Grafenberg I have not 
found in any of the embryos I have examined, although I find, as he describes, 
an early transitory union between the anlages of the short head of the biceps 
and the gluteus maximus. 
