600 THE NERVOUS SYSTEM. : 
(1) Muscular branches to the quadratus (4) Genito-crural. 
lumborum and psoas. (5) External cutaneous. 
(2) Iho-hypogastric. (6) Obturator. 
(3) [lio-inguinal. (7) Anterior crural. 
The nerves to the quadratus lumborum muscle arise independently from the 
first three or four lumbar nerves (and sometimes also from the twelfth thoracic 
nerve). The nerves to the psoas muscles arise from the second and third lumbar 
nerves, with additions, in some cases, from the first or fourth. They are often 
associated in their origin with the nerve to the iliacus from the anterior crural. The 
psoas minor, when present, is innervated by the highest of the nerves in question. 
The ilio-hypogastric and ilio-inguinal nerves closely resemble in their course 
and distribution the lower thoracic nerves, with which they are in series. 
The ilio-hypogastric nerve (n. ilio-hypogastricus) is the highest branch of 
the first lumbar nerve. It receives fibres also from the twelfth thoracic, when that 
nerve communicates with the first lumbar nerve. After traversing the psoas muscle 
obliquely, it appears at its outer border on the surface of the quadratus lumborum 
and behind the kidney. It courses through the loin, lying between the transversalis 
and obliquus internus muscles, above the crest of the ilium. About an inch in front of 
the anterior superior spine it pierces the obliquus internus, and continues its course 
in the groin beneath the aponeurosis of the obliquus externus. It finally becomes — 
cutaneous in the anterior abdominal wall, by piercing the aponeurosis of the obliquus 
externus about an inch and a half above the external abdominal ring (Fig. 442, p. 605). 
Its branches are—(1) muscular to the muscles of the abdominal wall; and (2) 
cutaneous branches, two in number. The iliac branch corresponds with the lateral 
branch of an intercostal nerve, and, after piercing the obliquus internus and 
obliquus externus, becomes cutaneous just above the iliac crest, below and behind 
the iliac branch of the last thoracic nerve. It is small, and may be absent. It is 
distributed to the skin over the upper part of the outer side of the buttock, in con- 
tinuity with the cutaneous branch of the posterior primary division of the first 
lumbar nerve. The hypogastric branch is the anterior terminal branch of the nerve. 
It supplies the skin of the anterior abdominal wall below the level of the last 
thoracic nerve and above the pubis. 
The ilio-inguinal nerve (n. ilio-inguinalis) is the second branch given off 
from the first lumbar nerve. It also may receive fibres from the last thoracic 
nerve. Not unfrequently the ilio-hypogastric and ilio-inguinal nerves are repre- 
sented for a longer or shorter part of their course by a single trunk. When separate 
the nerve takes a course similar to that of the ilio- hypogastric nerve, but at a lower 
level, as far as the anterior abdominal wall. It then pierces the obliquus internus 
further forward and lower down than the ilio-hypogastric ; and coursing forwards 
beneath the aponeurosis of the obliquus externus, just above Poupart’s ligament, it 
becomes superficial after passing through the external abdominal ring and external 
spermatic fascia (Fig. 442, p. 605). 
Its branches are muscular to the muscles of the abdominal wall, among which it 
passes, and cutaneous branches, which innervate the skin (1) of the anterior abdominal 
wall over the symphysis pubis, (2) of the thigh over the upper and inner part of 
Scarpa’s triangle, and (3) of the upper part of the scrotum, and root and dorsum of 
the penis (of the mons Veneris and labiura majus in the female). These last-named 
branches are contiguous to branches of the pudendal and pudic nerves. No lateral 
cutaneous branch arises from the ilio-inguinal nerve. It thus corresponds, like the 
hypogastric part of the ilio-hypogastric nerve, to the anterior trunk of a typical 
thoracic nerve. 
The genito-crural nerve (n. genito-femoralis) usually arises by two independent 
roots from the front of the first and second lumbar nerves, which unite in the substance 
of the psoas to form a slender trunk. It appears on the posterior abdominal wall, 
lying on the psoas magnus, internal to the psoas parvus, and, piercing the psoas 
fascia, it extends downwards on the outer side of the common and external iliac vessels 
and behind the ureter to Poupart’s ligament (Fig. 440, p. 599). Ata variable point 
above that ligament it divides into genital and crural branches. The genital branch 
is a minute nerve. It crosses the terminations of the external iliac vessels, and, 
