288 The Nerves and Muscles of the Leg 
nerve they seem to have a fairly direct path of growth. From the dorsal 
surface of the tibial nerve the calcaneal branch may be seen taking its 
rise. 
b. Variation. 
1. N. Cutaneus Femoris Posterior (small sciatic). 
This nerve shows considerable variation in origin and distribution. 
a. ORIGIN FROM SACRAL PLEXUS.—As stated in most text-books, it com- 
monly arises from the 26th, 27th, and 28th spinal nerves (1st, 2d, and 3d 
sacral). It may, however, arise from the (25th) and 26th; (25th), 26th, 
and 27th; 26th and 27th; (25th), 26th, 27th, and 28th; 27th and 28th, 
or from the (27th), 28th, and 29th spinal nerves. In table XII the fre- 
quency of these various modes of origin is shown. It is possible that in 
some of the instances tabulated the origin of the posterior cutaneous 
nerve was more extensive than the tabulation charts show, because in 
tracing back a nerve to the spinal roots from which it springs, small 
bundles of nerve fibres are sometimes torn. It is believed, however, that 
the chief roots of the nerve are indicated in the charts from which the 
table was made. It is to be noted that while an anterior position of the 
roots of the posterior cutaneous nerve of the thigh usually corresponds 
with an anterior position ef the lumbo-sacral plexus, this correspondence 
is not perfect. 
In these variations no special relations to race, sex, or side of body are 
apparent in the charts tabulated. 
According to A. Soulie (Poirier and Charpy, or), the branch from the 
2d sacral nerve to the posterior cutaneous nerve is constant while branches 
from the Ist and 3d are less constant and occasionally one may find a 
branch from the 4th sacral. 
There is great variation in the extent to which the roots and the trunk 
of the posterior cutaneous nerve are bound up with neighboring nerve 
trunks, such as the inferior gluteal, sciatic and pudic nerves. As a rule, 
however, the union between these trunks is so slight that they may be 
readily separated. It has not seemed, therefore, worth while to attempt 
a tabulation of relations of this sort. Not infrequently (in about 25% 
of instances) the perineal rami arise from a trunk which springs by 
special roots from the plexus. See table XIII. 
b. DistrrpuTion.—Gluteal branches (nn. clunium inferiores). These 
most commonly arise from a single branch given off from the posterior 
cutaneous nerve while this lies beneath the gluteus maximus muscle. This 
branch may pass up over the lower margin of the muscle before dividing 
into terminal rami (31 out of 77 instances) or it may divide into two or 
more rami which pass out under and turn back over the muscle in several 
