Page:Encyclopædia Britannica, Ninth Edition, v. 1.djvu/925

Rh SYSTEM.] IUo-inguinal, which supplies the skin of the groin; this nerve is by some said to send a branch to the internal oblique muscle ; c, External Cutaneous, which supplies the skin on the outer aspect of the thigh. The Mixed branches are as follows : a, Genito-crural, which supplies the cre- master muscle, and a cutaneous branch to the skin of the groin, b, Anterior Crural, a large nerve which enters the thigh by passing behind Poupart s ligament, and supplies the great extensor muscles of the knee-joint, and also the sar- torius, the psoas-iliacus and the pectineus, which act as flexors of the hip-joint; it gives off the following cutaneous branches : An internal cutaneoiis to the skin of the inner side, a middle cutaneous to the skin of the middle of the front of the thigh, and the long sapJienous nerve, which supplies the skin of the inner side of the knee-joint, the inner side of the leg and the foot, c, Obturator nerve, which leaves the pelvis through the obturator foramen, and sup plies tlie obturator externus and adductor muscles of the thigh, and sends a branch to the pectineus; it also supplies the hip and knee joints, and not unfrequently gives a branch to the skin of the lower part of the inner side of the thigh, d, An Accessory Obturator nerve is sometimes present, which goes to the pectineus, to the hip-joint, and also joins the obturator nerve. the spinal nerves; c, the last of these ganglia, called coccygeal ganglion, or ganglion impar; 6, position of solar plexus; 1, ilio-hypogastric nerve; 2, ilio- inguinal; 3, external cutaneous; 4, genito-crural ; 5, anterior crural; 6, obturator 7 suerior lutsea The Lumbo-sacral Cord is formed of the fifth lumbar nerve and of a branch from the fourth lumbar. It joins the sacral plexus. Before the junction it gives origin to a com municating and a muscular branch. The Communicating joins the fifth lumbar ganglion of the sympathetic. The Muscular, branch, named the superior glutceal nerve, sup plies the glutncus medius and minimus and the tensor fascite femoris muscle. The Sacral plexus is situated in the cavity of the pelvis, and is the largest of all the plexuses. It is formed by the 869 junction of the lumbo-sacral cord, the first, second, third, and partof the fourth sacral nerves, and appears as a flattened mass in front of the sacrum. It gives origin to com municating, muscular, and mixed branches. The Com~ municating branches join the upper sacral ganglia of tho sympathetic system. The Muscular branches supply the upper fibres of the glutaeus maximus, the pyriformis, gemelli, quadratus femoris, and obturator interims muscles. The Mixed nerves are as follows : a, Pudic, which supplies the muscles and skin of the external organs of generation, b, Small Sciatic, which supplies not only the lower fibres of the glutsous maximus muscle, but the skin of the buttock, the back of the thigh, of the popliteal space, and of the leg ; it also gives a long pudendal branch to the skin of the perineum, c, Great Sciatic; this is the largest nerve in the body. It leaves the pelvis through the great sciatic foramen, and passes down the back of the thigh, when it divides into external and internal popliteal branches. Before dividing it supplies the hamstring muscles, and gives a branch to the adductor magnus. The external popliteal branch gives offsets to the knee- joint, passes down the outer side of the leg, supplies the peronei longus and brevis, gives off the communicant peronei branch to the skin of the outer side of the back of the leg, and ends as the external cutaneous nerve for the dorsuni of the foot and the dorsal surfaces of all the toes, except the outer side of the little and the adjacent sides of the great and second toes. The internal popliteal branch gives offsets to the knee-joint, and supplies the communi cant tibialis nerve, which joins the comnmnicans peronei, and forms with it the external sapJienous nerve that passes to the outer side of the foot and little toe. The internal popliteal also supplies the muscles of the calf and the popliteus muscle, and is prolonged downwards as the posterior tibial nerve. The anterior tibial passes to the front of the leg, supplies the tibialis anticus, peroneus ter- tius, and extensor muscles of the toes, and terminates as the cutaneous digital nerve for the adjacent sides of the great and second toes. The posterior tibial nerve passes down the back of the leg, supplies the tibialis posticus and long flexors of the toes, gives off a cutaneous branch to the skin of the heel, and terminates by dividing into the internal and external plantar nerves. The internal plantar nerve supplies the skin of the sole and sends digital branches to the skin of the great, second, third, and tibial side of the fourth toes ; it also supplies the abductor pollicis, flexor brevis digitorum, flexor brevis pollicis, and two inner lumbrical muscles. The external plantar nerve supplies digital branches to the skin of the little and fibular sides of the fourth toes, and branches to all the muscles of the sole of the foot which are not supplied by the internal plantar nerve. The Sacro-Coccygeal is the smallest plexus belonging to the anterior divisions of the spinal nerves. It is formed by a part of the fourth sacral, the fifth sacral, and the coccygeal nerves. It lies in front of the last sacral and the first coccy geal vertebra, and gives origin to communicating, visceral, muscular, and cutaneous branches. The Communicating branches join the lower sacral and the coccygeal ganglia of the sympathetic system ; the Visceral pass to the pelvic plexus of the sympathetic, and through it to the bladder and rectum ; the Muscidar to the levator ani, coccygeus, and sphincter ani externus muscles : the Cutaneous to the skin about the anus and tip of the coccyx. THE BRAIN. By the term BRAIX or ENCEPHALON is Brain, meant all that part of the central nervous axis which is contained within the cavity of the skull. It is divided into several parts, named medulla oblongata, pons, cere bellum, and cerebrum. The medulla oblongata is directly