eo 
~ 
Ce 
Charles R. Bardeen 
Ventrally the genital nerve, usually after anastomosing with the in- 
guinal, passes along the vaginal process through the aponeurosis of the 
external oblique and over the inguinal ligament to the thigh. It is inter- 
esting to note that this development considerably precedes the descent 
of the testicle. 
In Plate VI, Fig. 2, the border nerves of Embryo XXII, length 20 
mm., are pictured. It is somewhat difficult to trace with certainty the 
border nerves in this embryo, but the figure is believed to illustrate ap- 
proximately the actual relations. While in Embryo CXLIV a consider- 
able interval separates the anlage of the iliac crest from the distal margin 
of the abdominal musculature, in Embryo XXII the crest is much fur- 
ther developed and at the same time has been rotated toward the dorsal 
portion of the distal margin of the oblique abdominal musculature. This 
at the same time has extended distally and become attached to the iliac 
erest. Meanwhile the peritoneal wall has bulged laterally so that the 
fascial extension of the transversus muscle covers the ilio-psoas muscle 
in the region of the pelvis and the transversus muscle has formed its 
pelvic attachments. The main trunks of the border nerves have been 
brought by these changes into relations which closely resemble those char- 
acteristics of the adult. Adult conditions are reached by some further 
relative shifting of parts and by the growth of the nerves within the 
areas for which they are destined. 
The segmental relations of the border nerves may be best understood 
by comparing the position of the pelvie girdle when the nerves first ex- 
tend toward the skin with the condition brought about by the shifting of 
the girdle. See Plates III, 1V, V and VI. In Embryo CIX, the stage in 
which the nerves first extend toward the skin, the border nerves arise 
from the spinal nerves in the following order: iliohypogastric, inguinal, 
genital and lumbo-inguinal. As these nerves grow forward there takes 
place a rotation of the base of the hmb medially, ventrally and posteriorly. 
At the same time the spinal column becomes straightened and the limb- 
bud as a whole descends posteriorly. The pubis is carried from a point 
opposite the 21st (12th thoracic) segment to a point opposite the 26th, 
and at the same time the posterior margin of the ilium is usually brought 
to lie opposite the 26th and 27th vertebra to which it becomes attached. 
The two pubes are carried forward ventrally until they are united by the 
symphysis pubis. 
As the pubis rotates ventrally and posteriorly the inferior portion of 
the abdominal wall is extended in a corresponding direction. The ven- 
