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their union the nervus suralis results, which reaches the foot, winding round the back of the lateral malleolus, along with the small saphenous vein. · The nervus suralis supplies cutaneous branches to the lateral side and back of the distal third of the leg, the ankle and heel, and the side of the foot and little toe, as well as articular branches to the ankle and tarsal joints.
FIG. 629.- DISTRIBUTION OF CUTANEOUS NERVES ON THE BACK OF THE LOWER LIMB.
In A the distribution of the several nerves is represented, their names being given. In B 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 centre.
The nervus suralis communicates on the foot with the superficial peroneal nerve, and its size varies with the size of that nerve. It may extend on to the dorsum of the foot for a considerable dist: and may either reinforce or replace the branches of the abovenamed nerve to the intervals between the fourth and fifth and the third and fourth toes. The mode of formation of the nervus suralis is very variable. The usual arrangement is that described. Frequently the peroneal anastomotic nerve and the medial sural nerve (medial cutaneous nerve of the leg) do not unite, and in such cases the more usual arrangement is for the tibial trunk alone to form the nervus suralis (nerve of the calf),
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 (0.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 third of the thigh on the medial side. It supplies the skin of the distal half of the thigh, extending as far as the knee, where it joins in the formation of the patellar plexus.
The distal branch represents the termination of the nerve. It passes along the medial side of the thigh over the sartorius muscle, and communicates in the middle third of the thigh with the saphenous and obturator nerves to form the obturator plexus. Piercing the fascia lata on the medial side of the thigh in the distal third, it ramifies over the side of the knee, and assists in the formation of the patellar plexus.
The size of the medial cutaneous nerve varies with the size of the cutaneous part of the obturator, and of the saphenous nerve.
N. Saphenus.—The saphenous nerve may be regarded as the terminal branch of the femoral nerve. It is destined for the skin of the leg and foot. From its origin in the femoral triangle it extends distally alongside the femoral vessels to the adductor canal. In the canal it crosses obliquely over the femoral sheath from lateral to medial side. At the distal end of the canal, accompanied by the saphenous branch of the arteria genu suprema, it passes over the tendon of the adductor magnus, and opposite the medial side of the knee-joint becomes cutaneous by passing between the sartorius and gracilis muscles. The nerve then extends distally in the leg along with the great saphenous vein, and coursing over the front of the medial malleolus it terminates at the middle of the medial border of the foot.
Branches.—1, A communicating branch arises in the adductor canal, and, passing medially behind the sartorius, joins with branches of the obturator nerve in forming the obturator plexus.
2. Ramus Infrapatellaris.--The infra-patellar branch arises at the distal end of the adductor canal, and piercing the sartorius muscle is directed distally and forwards below the patella, and over the medial condyle of the tibia to the front of the knee and proximal part of the leg. It enters into the formation of the patellar plexus.
3. An articular branch sometimes arises from the nerve at the medial side of the knee.
4. Rami Cutanei Cruris Mediales.—The terminal branches of the saphenous nerve are distributed to the skin of the front and medial side of the leg and the posterior half of the dorsum and medial side of the foot.
Plexus Patellaris. — The patellar plexus consists of fine communications beneath the skin in front of the knee, between the branches of the cutaneous nerves supplying that region. The nerves which enter into its formation are the infra-patellar branch of the saphenous, medial and intermediate cutaneous nerves, and sometimes the lateral cutaneous nerve of the thigh.
The accessory obturator nerve (n. obturatorius accessorius) is only occasionally present (29 per cent., Eisler). It arises from the third, or third and fourth lumbar nerves, between the roots of the obturator and femoral nerves. Associating itself with the obturator, from which, however, it is quite separable, it appears in the abdomen at the medial side of the psoas muscle, and coursing over the pelvic brim behind the external iliac vessels, it leaves the obturator nerve, and enters the thigh in front of the os pubis.
In the thigh, behind the femoral vessels, it usually ends in three branches : a nerve which replaces the branch from the femoral nerve to the pectineus, a nerve to the hip-joint, and a nerve which communicates with the superficial part of the obturator nerve. In some cases it only supplies the nerve to the pectineus; more rarely it is of considerable size, and reinforces the obturator nerve in the innervation of the adductor muscles.
The accessory obturator nerve was first described by Winslow as the n. accessorius anterioris cruralis. Schmidt later described it in great detail, and gave it the name it now bears. It is more closely associated with the femoral than with the obturator. Its origin is behind the roots of the obturator: it is separated, like the femoral, from the obturator by the pubic bone, and its chief branch, to the pectineus muscle, replaces the normal branch from the femoral nerve. On the other hand, for a part of its course it accompanies the obturator, and in rare cases it may replace branches of that nerve.
The sacral portion of the lumbo-sacral plexus is destined almost entirely for the lower limb. It is usually formed by the anterior rami of a part of the fourth lumbar nerve (n. furcalis), the fifth lumbar, the first, and parts of the second, and third sacral nerves (n. bigeminus).
Communications with the Sympathetic.- Each of the nerves named is connected to the lumbar or pelvic sympathetic by gray rami communicantes, as already described ; and white rami communicantes pass from the third and usually also from the second or fourth sacral nerves to join the pelvic plexus of the sympathetic.
Position and Constitution.—The plexus is placed on the posterior wall of the pelvis between the parietal pelvic fascia and the piriformis muscle. In front of it are the pelvic colon, the hypogastric vessels, and the ureter.
The plexus is constituted by the convergence of the nerves concerned towards the inferior part of the greater sciatic foramen, and their union to form a broad triangular band, the apex of which is continued through the greater sciatic foramen below the piriformis muscle into the buttock, as the sciatic nerve. From the anterior and posterior surfaces of this triangular band numerous small branches arise, which are distributed to the parts in the neighbourhood of the origin of the nerve.
The sciatic nerve ends in the thigh by dividing into two large nerves, the tibial (O.T. internal popliteal), and common peroneal (O.T. external popliteal). In many cases these two nerves are distinct at their origin, and are separated sometimes by fibres of the piriformis muscle. In all cases, on removal of the sheath investing the sciatic nerve, the tibial and peroneal nerves can be traced up to the plexus, from which they invariably take origin by distinct and separate roots.
Formation. The descending branch of the fourth lumbar nerve (n. furcalis) after emerging from the border of the psoas major muscle, medial to the obturator nerve, divides behind the iliac vessels into anterior and posterior (ventral and dorsal) parts, each of which joins a corresponding part of the fifth lumbar nerve. The anterior ramus of the fifth lumbar nerve descends over the ala of the sacrum, and divides into anterior and posterior parts, which are joined by the corresponding parts of the fourth lumbar nerve. The two resulting trunks are sometimes called the truncus lumbosacralis or lumbo-sacral trunk. The first and second sacral nerves pass almost horizontally laterally from the anterior sacral foramina, and divide in front of the piriformis into similar anterior and posterior parts. The third sacral nerve (n. bigeminus) divides into superior and inferior parts. The inferior part is concerned in forming the pudendal plexus. The superior part is directed laterally, and slightly upwards, towards the second nerve, and does not separate into two parts, but remains undivided.
These trunks combine to form the sacral plexus, and its main subdivisions, in the following way. Lying in apposition, and converging to the lower part of the greater sciatic foramen, the posterior (dorsal) trunks of the fourth and fifth lumbar nerves (lumbo-sacral trunk), and of the first and second sacral nerves, combine to form the common peroneal nerve and the subordinate nerves which arise from the posterior aspect of the plexus. The anterior (ventral) trunks of the fourth and fifth lumbar nerves (lumbo-sacral trunk), and of the first and second sacral nerves, together with that part of the third sacral nerve which is contributed to the plexus, unite to form the tibial nerve and the subordinate nerves arising from the front of the plexus.
Of these nerves the fifth lumbar and first sacral are the largest; the others diminishing in size as they are traced upwards and downwards. There is no distinct demarcation between the sacral and pudendal plexuses. The second and third sacral nerves (and in some cases the first sacral also) are concerned in the formation of both plexuses.
Branches.— The nerves of distribution derived from the sacral plexus &re divided according to their origin into an anterior (ventral) and a posterior (dorsal)