374 The Nerves and Muscles of the Leg 
tibial nerves in the thigh are separated by a considerable amount of dense 
tissue. 
There is much variation in the number and position of the spinal 
nerves which supply the main nerve trunks of the limb as well as in those 
which supply the smaller branches which pass directly from the plexus 
to the gluteal muscles and the piriformis. There is also great variation 
in the number, course and distribution of the branches which pass from 
the main nerve trunks to the muscles and the skin. No correlation has 
been discovered between variation in the source of supply and variation 
in peripheral distribution of the intrinsic nerves of the limb, with the 
exception of the cutaneous border nerves. No marked correlations have 
been discovered between either sort of variation-and race, sex, or side of 
body. 
While the development of the musculature is fairly direct, there is 
probably as much correlation between the ontogeny and phylogeny of the 
muscles of the leg as between the ontogeny and phylogeny of the skeleton. 
D. PERINEAL MUSCULATURE AND THE NERVES OF THE 
PUDIC GROUP. 
a. Embryonic Development. 
In an embryo of 11 mm. (Plate III, Fig. 1) the sacral plexus is fully 
formed and several branches may be seen extending out toward the cloaca 
and viscera. These branches indicate the developing pudic and visceral 
nerves, but differentiation has not proceeded sufficiently far to make it 
possible to determine with certainty what each of the branches represents. 
The myotomes of the sacro-coccygeal region are distinct. No specific 
differentiation of the perineo-caudal musculature is apparent.. The rela- 
tions of the pubic nerves to the nerves of the leg are shown schematically 
in Plate ITI, Fig. 3. 
In a slightly older embryo (Plate X, Fig. 1) the main branches of the 
pudic and visceral nerves have appeared. The dorsal nerve of the penis 
arises in the main from the 3d sacral nerve. The perineal nerves arise 
from the (2d), 3d, and 4th sacral nerves. The hemorrhoidal nerve arises 
from the 3d and 4th sacral nerves. About the region of the cloaca there 
is some condensation of tissue, but there is no distinct differentiation of 
muscle. From the 3d and 4th sacral nerves branches are given to a highly 
developed visceral plexus in which a large amount of chromophile tissue 
is apparent. This tissue mass lies lateral to the intestine and extends 
