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above the inguinal ligament, it becomes superficial after passing through the subcutaneous inguinal ring and external spermatic fascia (Fig. 623, p. 715).
Its branches are muscular to the muscles of the abdominal wall, among which it passes, and cutaneous branches (anterior scrotal, or labial nerves), which innervate
the skin (1) of the anterior abdominal wall over the symphysis pubis, (2) of the thigh over the proximal and medial part of the femoral triangle, and (3) of the superior part of the scrotum, and root and dorsum of the penis (of the mons Veneris and labium majus in the female). These last-named branches are contiguous to branches of the perineal and pudendal nerves. No lateral cutaneous branch arises from the ilio-inguinal nerve. It thus corresponds, like the anterior cutaneous part of the ilio-hypogastric nerve, to the anterior trunk of a typical thoracic nerve.
N. Genitofemoralis.-The genito-femoral nerve (O.T. genito-crural) usually arises by two independent roots from the front of the first and second lumbar nerves, which unite in the substance of the psoas major to form a slender trunk. It appears on the posterior abdominal wall, lying on the psoas major, medial to the psoas minor, and, piercing the psoas fascia, it extends downwards on the lateral aspect of the common and external iliac vessels and behind the ureter, to the inguinal ligament (Fig. 625, p. 721). At a variable point above that ligament it divides into two branches. 1. The external spermatic branch is a small nerve. It crosses the terminations of the external iliac vessels, and, along with the ductus deferens and testicular and external spermatic vessels, enters the inguinal canal through the abdominal inguinal ring. It terminates by supplying small branches to the skin of the scrotum and adjacent part of the thigh. In the female it accompanies the round ligament to the labium majus. This nerve gives off in its course the following small branches: (1) to the external iliac artery; (2) to the cremaster muscle; (3) to communicate with the spermatic plexus of the sympathetic. 2. The lumbo-inguinal branch continues the course of the parent nerve into the thigh, lying on the lateral aspect of the femoral artery. It becomes cutaneous by passing through the fossa ovalis or through the iliac portion of the fascia lata, and supplies an area of skin over the femoral triangle, lateral to that supplied by the ilio-inguinal nerve (Fig. 623, p. 715). It communicates in the thigh with the intermediate cutaneous branch of the femoral nerve. Before piercing the deep fascia it gives a minute branch to the femoral artery.
N. Cutaneus Femoris Lateralis.-The lateral cutaneous nerve of the thigh is distributed only to the skin (Fig. 625). It arises from the back of the lumbar plexus, and usually from the second and third lumbar nerves. Emerging from the lateral border of the psoas major muscle, the nerve crosses the iliacus muscle, beneath the fascia iliaca, to reach the anterior superior iliac spine. It enters the thigh beneath the lateral end of the inguinal ligament, and either over, under, or through the origin of the sartorius muscle. It extends distally along the front of the thigh for a few inches, lying at first beneath the fascia lata, and afterwards in a tubular investment of the fascia. It gives off small branches in this part of its course, and finally, piercing the fascia about four inches distal to the anterior superior iliac spine, it separates into anterior and posterior terminal branches. The anterior branch is the larger, and is distributed on the lateral aspect of the front of the thigh almost to the knee. The smaller posterior branch supplies the skin of the lateral side of the buttock, distal to the greater trochanter, and the skin of the proximal twothirds of the lateral aspect of the thigh (Fig. 625, p. 721).
The obturator nerve supplies the muscles and skin on the medial side of the thigh. It arises in the substance of the psoas major muscle by three roots placed in front of those of the femoral nerve, and derived from the second, third, and fourth lumbar nerves (Fig. 624, p. 718). Sometimes the root from the second nerve is absent. Passing vertically downwards, the nerve emerges from the psoas major at its medial border, behind the common iliac, and on the lateral side of the hypogastric vessels. It passes forwards below the pelvic brim in company with the obturator artery to the obturator groove of the obturator foramen, through which it reaches the thigh. While in the obturator groove it separates into its two main branches, named anterior and posterior (Fig. 626, p. 723).
The anterior (O.T. superficial) branch enters the thigh in front of the obturator externus and adductor brevis muscles, and behind the pectineus and adducto: longus. In the middle third of the thigh it is found coursing along the medial border of the adductor longus, anterior to the gracilis; and it finally divides into two slender terminal filaments, of which one enters the adductor canal and ends on the femoral artery, while the other supplies the skin for a variable distance on the medial side of the thigh and joins in the obturator plexus.
The branches of the anterior part of the nerve are:
1. An articular branch to the hip-joint, which arises from the nerve as soon as it enters the thigh, and supplies the joint through the acetabular notch.
2. Muscular branches to the adductor longus, gracilis, adductor brevis (usually), pectineus (occasionally). The last-named muscle is not usually supplied from the obturator nerve.
3. A cutaneous branch of very variable size forms one of the terminal branches (Fig. 626). It becomes superficial between the gracilis and adductor longus, in the middle third of the thigh, and may supply the skin of the distal two-thirds of the thigh on its medial side. It is generally of small size, and is connected with branches of the medial cutaneous and saphenous nerves behind the sartorius muscle to form the obturator (O.T. sub-sartorial) plexus. The branch from the saphenous nerve to the plexus passes medially behind the sartorius after piercing the
FIG. 626.-SCHEME OF THE COURSE AND DISTRIBUTION OF THE OBTURATOR NERVE.
aponeurotic covering of the adductor canal. The branch from the medial cutaneous nerve is generally superficial at the point of formation of the plexus.
4. The branch to the femoral artery is the other terminal branch of the nerve. It enters the adductor canal along the medial border of the adductor longus, and ramifies over the distal part of the artery.
5. A fine communicating branch sometimes joins the femoral nerve in front of the hip-joint.
The posterior (O.T. deep) branch of the obturator nerve reaches the thigh by piercing the obturator externus muscle. It passes distally between the adductor brevis and adductor magnus muscles. After passing obliquely through the adductor magnus, it appears in the popliteal fossa on the popliteal vessels, and terminates by piercing the oblique ligament of the knee and supplying the kneejoint.
Its branches are:-(1) muscular branches to the obturator externus, adductor magnus, and (when the muscle is not supplied by the superficial part of the nerve)
the adductor brevis. The branch to the obturator externus arises before the nerve enters the muscle, in the obturator groove. The nerve to the adductor magnus is given off as the obturator nerve passes through the substance of the muscle. (2) An articular terminal branch is supplied to the posterior aspect of the knee-joint.
The femoral nerve (O.T. anterior crural) is the large nerve for the muscles and skin of the front of the thigh. It arises in the substance of the psoas major muscle, from the back of the second, third, and fourth lumbar nerves, posterior to the obturator nerve. Passing obliquely through the psoas major muscle, it emerges from its lateral border in the pelvis major (Fig. 625, p. 721). Passing downwards in the groove between the psoas and iliacus, it enters the thigh beneath the inguinal ligament, lateral to the femoral sheath and femoral vessels. In the femoral triangle it breaks up into a large number of branches, among which the lateral circumflex artery of the thigh passes in a lateral direction.
The branches of the femoral nerve, which are (1) muscular, (2) articular, and (3) cutaneous, arise in the following way :
In the abdomen a muscular branch arises from the lateral aspect of the nerve and enters the iliacus muscle.
In the femoral triangle the terminal muscular, articular, and cutaneous branches arise in the form of a large bundle of nerves.
1. Rami Musculares.-The muscular branches supply the pectineus, sartorius, and quadriceps. The nerve to the pectineus arises close to the inguinal ligament, and, coursing obliquely distally and medially behind the femoral vessels, enters the muscle at its lateral border. It is not infrequently double. It sometimes gives off a fine communicating branch to the anterior part of the obturator nerve. The nerves to the sartorius are in two sets: a lateral, short set of nerves, associated with the lateral part of the intermediate cutaneous nerve, which supply the proximal part of the muscle; and a medial, longer set, which are associated with the medial part of the intermediate cutaneous nerve, and enter the middle of the muscle. The parts of the quadriceps are supplied by several branches. The vastus lateralis and rectus femoris are supplied on their deep surface by separate nerves which are accompanied by branches of the lateral circumflex artery of the thigh. The vastus intermedius muscle is supplied superficially by a nerve which passes through the muscle, and innervates also the muscle of the knee-joint (subcrureus). It also receives fibres from one of the nerves to the vastus medialis. The vastus medialis muscle is supplied by two nerves: a proximal trunk, which supplies the proximal part of the muscle, and sends fibres to the vastus intermedius as well; and a distal trunk, which descends on the lateral side of the femoral artery along with the saphenous nerve, and passing beneath the sartorius, over or under the aponeurotic covering of the adductor canal, enters the medial side of the muscle. This nerve gives off a small branch which enters the medullary canal of the femur.
2. The articular branches supply the hip and knee-joints. The articular branch to the hip-joint arises from the nerve to the rectus femoris, and is accompanied by branches from the lateral circumflex artery of the thigh. The articular branches to the knee-joint are four in number. Three of them arise from the nerves to the vastus lateralis, vastus intermedius, and vastus medialis, which, after the muscular nerves are given off, are continued downwards to the knee-joint along the front of the femur. A fourth articular branch arises (sometimes) from the saphenous nerve. 3. Rami Cutanei Anteriores. The cutaneous branches are the intermediate and medial cutaneous, and the saphenous nerves (Fig. 627).
The intermediate cutaneous nerve arises in two parts, a lateral and a media! branch, in the proximal part of the femoral triangle. The two branches descend vertically and become cutaneous by piercing the fascia lata over the proximal third of the sartorius muscle. They carry muscular branches to the sartorius, and the lateral branch in many cases pierces the muscle. These two nerves supply the skin of the distal three-fourths of the front of the thigh, between the lateral cutaneous nerve of the thigh laterally and the medial cutaneous on the medial side. They
reach to the front of the patella, and there assist in the formation of the patellar plexus. The lateral branch communicates, in the proximal third of the thigh, with twigs from the lumbo-inguinal branch of the genito-femoral nerve.
The medial cutaneous nerve lies at first in the femoral triangle on the lateral side of the femoral vessels. At the apex of the triangle it crosses over the femoral vessels, and is directed distally over or through the sartorius muscle, and beneath
FIG. 627.-DISTRIBUTION OF CUTANEOUS NERVES ON THE FRONT OF THE LOWER LIMB. On the left side the distribution of the several nerves is represented in colour. On the right side a schematic representation is given of the areas supplied by the above nerves, the figures indicating the spinal origin of the branches of distribution to each area.
the fascia lata, to the distal third of the thigh. It is distributed to the skin of the distal two-thirds of the thigh on the medial side by means of three branches -proximal, middle, and distal.
The proximal branch may be represented by two or more twigs. It arises from the main nerve near its origin, and pierces the fascia lata near the apex of the femoral triangle. It is distributed to the skin of the proximal part of the thigh, along the line of the great saphenous vein. The middle or anterior branch is a larger nerve. It separates from the distal branch at the apex of the femoral triangle, and passing over the sartorius muscle becomes cutaneous in the middle