Ilio-inguinal, which supplies the skin of the groin; this junction of the lumbo-sacral cord, the first, second, third, nerve is by some said to send a branch to the internal and partof the fourth sacral nerves, and appears as aflattened oblique muscle; c, External Cutaneous, which supplies the mass in front of the sacrum. It gives origin to come skin on the outer aspect of the thigh. The Mixed branches municating, muscular, and mixed branches. The Comare as follows :-a, Genito-crural, which supplies the cre- municating branches join the upper sacral ganglia of the master muscle, and a cutaneous branch to the skin of the sympathetic system. The Muscular branches supply the groin. b, Anterior Crural, a large nerve which enters the upper fibres of the glutæus maximus, the pyriformis, thigh by passing behind Poupart's ligament, and supplies the gemelli, quadratus femoris, and obturator internus great extensor muscles of the knee-joint, and also the sar muscles. The Mixed nerves are as follows :a, Pudic, torius, the psoas-iliacus and the pectineus, which act as which supplies the muscles and skin of the external organs flexors of the hip-joint; it gives off the following cutaneous of generation. b, Small Sciatic, which supplies not only the branches : An internal cutaneous to the skin of the inner lower fibres of the glutæus maximus muscle, but the skin of side, a middle cutaneous to the skin of the middle of the the buttock, the back of the thigh, of the popliteal space, front of the thigh, and the long saphenous nerve, which and of the leg; it also gives a long pudendal branch to supplies the skin of the inner side of the knee-joint, the the skin of the perineum. c, Great Sciatic; this is the inner side of the leg and the foot. c, Obturator nerve, which largest nerve in the body. It leaves the pelvis through leaves tho pelvis through the obturator foramen, and sup- the great sciatic foramen, and passes down the back of the plies the obturator externus and adductor muscles of the thigh, when it divides into external and internal popliteal thigh, and sends a branch to the pectineus; it also supplies | branches. Before dividing it supplies the hamstring the hip and knee joints, and not unfrequently gives a muscles, and gives a branch to the adductor magnus. branch to the skin of the lower part of the inner side of The external popliteal branch gives offsets to the knee. the thigh. d, An Accessory Obturator nerve is sometimes joint, passes down the outer side of the leg, supplies the present, which goes to the pectineus, to the hip-joint, and peronei longus and brevis, gives off the communicans also joins the obturator nerve.

peronei branch to the skin of the outer side of the back of the leg, and ends as the external cutaneous nerve for the dorsum 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 communicans tibialis nerve, which joins the communicans peronei, and forms with it the external saphenous nerve that passes to the outer side of the foot and little toe. The internal popliteal also supplies the muscles of the call 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 tertius, 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 Fig. 66.-Lumbar, sacral, and sacro-coccygen. plexuses. DXII, the lowest thoracic nerve of the intercostal series; LI to IV, the nerves of the lumbar plexus; V, part of the fourth sacral, the fifth sacral, and the coccygeal the fifth lumbar, with 8, the lumbo-sacral cord; SI to IV, sacral nerves going

It lies in front of the last sacral and the first coccyto form the sacral plexus;. V and CI, the sacro-coccygeal plexus; a, chain of ganglia of the sympathetic system, showing the communicating branches with geal vertebræ, and gives origin to communicating, visceral, inguinal; 3, external cutaneous ; 4, genito-crural; 5, anterior crural; 6, branches join the lower sacral and the coccygeal ganglia of ganglion impar; o, position of solar plexus; 1,'ilio-hypogastric nerve; 2, ilio muscular, and cutaneous branches. The Communicating obturator; 7, superior glutæal.

the sympathetic system ; the Visceral pass to the pelvic The Lumbo-sacral Cord is formed of the fifth lumbar plexus of the sympathetic, and through it to the bladder nerve and of a branch from the fourth lumbar. It joins the and rectum ; the Muscular to the levator ani, coccygeus, sacral plexus. Before the junction it gives origin to a com and sphincter ani externus muscles; the Cutaneous to the municating and a muscular branch. The Communicating skin about the anus and tip of the coccyx. joins the fifth lumbar ganglion of the sympathetic. The Muscular. branch, named the superior glutæal nerve, sup

The BRAIN.—By the term Brain or ENCEPHALON is Brain. plies the glutæus medius and minimus and the tensor fasciæ meant all that part of the central nervous axis which is femoris muscle.

contained within the vity of the skull. It is divided The Sacral plexus is situated in the cavity of the pelvis, into several parts, named medulla oblongata, pons, cereand is the largest of all the plexuses. It is formed by the belium, and cerebrum. The medulla oblongata is directly

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continuous with the spinal cord through the foramen direction. The fibres of the posterior median column of magnum. The cerebellum lies above, and immediately the cord are prolonged upwards as the posterior pyramid. behind the medulla oblongata, with which it is directly The fibres of the posterior column of the cord are for the continuous. The pons lies above and in front of the most part prolonged upwards into the restiform body, medulla, with which it is directly continuous. The cere- though some fibres pass to the front of the medulla to brum is the highest division, and lies above both pons and participate in the decussation of the anterior pyramids. cerebellum, with both of which it is directly continuous. The lateral column of the cord divides into three parts : Several figures of the brain are given in Plate XVIII. a, the greater number of its fibres pass inwards across the

The MEDULLA OBLONGATA rests upon the basi-occipital. anterior median fissure, to assist in forming the anterior It is somewhat pyramidal in form, about 14 inch long, and pyramid of the opposite side, so as to produce the decussation 1 inch broad in its widest part. It is a bilateral organ, and already referred to; b, others join the restiform body; C, is divided into a right and a left half by shallow anterior uthers form the fasciculus teres situated on the floor of the and posterior median fissures, continuous with the corre- | 4th ventricle. The antesponding fissures in the spinal cord; the posterior fissure rior column of the cord ends above in the 4th ventricle. Each half is subdivided | also divides into three into elongated tracts of nervous matter. Next to, and parts: a, some fibres parallel with the anterior fissure is the anterior pyramid form the arciform fibres (Pl. XVIII. figs. 1 and 2, P). This pyramid is continuous and join the restiform below with the cord, and the place of continuity is marked body; b, others assist in by the passage across the fissure of three or four bundles of the formation of the nerve fibres, from each half of the cord to the opposite olivary fasciculus; C,

biz anterior pyramid; this crossing is called the decussation of others are prolonged upthe pyramids. To the side of the pyramid, and separated wards in the anterior from it by a faint fissure, is the olivary fasciculus, which pyramid of the same at its upper end is elevated into the projecting oval-shaped side (Fig. 67). olivary body (Pl. XVIII, figs. 1 and 2, 0). Behind the olive, The anterior pyramid and separated from it by a faint groove, is the strong tract consists partly of fibres named restiform body; as it ascends from the cord it of the anterior column diverges from its fellow in the opposite half of the medulla of the cord of the same oblongata. By this divergence the central part of the side, partly of decusmedulla is opened up, and the lower half of the cavity of sating fibres of the antethe 4th ventricle is formed. Internal to the restiform body rior commissure, partly is the posterior pyramid, which is continuous with the of decussating fibres Fig. 67. - Diagrammatic dissection of the me

dulla oblongata and pons to show the coure postero-median column, and bounds the postero-median from the posterior co of the fibres. a, superficial, d', deep transverse fissure. Where the restiform bodies diverge from each lumns and posterior cor

fibres of the pons; b, b, anterior pyramide

ascending at through the pons; 4 C, olivary other, there also the posterior pyramids diverge outwards nu of grey matter, but bodies; é, olivary fasciculus in the pors;

d, d, anterior columns of cord; inner part from the sides of the postero-median fissure. At the upper principally of the decus

of the right column joining the anterie part of the floor of the 4th ventricle a longitudinal tract of sating fibres of the lateral

pyramid ; J, the outer part going to ite

olivary fasciculus; g, lateral column of ecid; nerve fibres, the fasciculus teres, ascends on each side of column of the opposite h, the part which decussates at k, the decussiits median furrow (Fig. 68, 7). Slender tracts of nerve side of the cord. The

tion of the pyramids; l, the part which joins

the restiform body ; m, that which forms ihe fibres, the arciform fibres, arch across the side of the medulla fibres of the anterior fasciculus teres; n, arciform fibres. land 2,

sensory and motor roots of fifth nerre; immediately below the olive ; and white slender tracts pyramid are prolonged 3, sixth nerve; 4, portio dura; 5. portio emerge from the median furrow of the 4th ventricle, pass through the pons to the

intermedia; 6, portio mollis of seventh nerre;

7, glosso-pharyngeal ; 8, pneumo-gastric; 9, outwards across its floor, and form the strive medullares or cerebrum. Owing to spinal accessory of eighth nerve; 10, hypo

glossal nerve. acousticæ, the roots of origin of the auditory nerve (Fig. 68,8). the decussation of the

The medulla oblongata, like the spinal cord, with which lateral columns of the cord in the formation of the pyramids, it is continuous, consists both of grey and white matter. the motor nerve fibres from one-half of the brain are transBut the exterior of the medulla is not so exclusively formed mitted to the opposite side of the cord, so that injuries of white matter as is the outer part of the cord, for the affecting one side of the brain occasion paralysis of the divergence from each other of the restiform bodies and motor nerves arising from the opposite half of the cord. posterior pyramids of opposite sides opens out the central | The olivary fasciculus is formed partly of fibres of the part of the medulla, and allows the grey matter to become anterior column of the same side, and partly of fibres superficial on the floor of the 4th ventricle. The nerve arising from the grey matter of the olive. It is continued fibres which enter into the formation of the pyramids and upwards through the pons to the cerebrum. The restiform the other tracts just described, are partly continuous below body is formed principally of fibres of the posterior column with the columns of the spinal cord, and are prolonged of the same side, but partly of fibres of the lateral columu, upwards either to the pons and cerebrum, or to the cere and also of the arciform fibres from the anterior column, bellum, or they partly take their rise in the medulla and from the grey matter of the superior and inferior oblongata itself from the cells of its grey matter. As the olives. As the restiform body is continued upwards to medulla is a bilateral organ, its two halves are united the cerebellum, and forms its inferior peduncles, the arciform together by commissural fibres, which cross obliquely its fibres have been called by Solly the superficial cerebellar mesial plane from one side to the other, and as they decus-fibres of the medulla. Through the restiform body the sate in that plane, they form a well-marked mesial band cerebellum is connected with the posterior, lateral, and or raphé. Further, the medulla is a centre of origin for anterior columns of the cord as well as with the olivary several pairs of the more posterior encephalic nerves, and for nuclei in the grey matter of the medulla oblongata. The the vaso-motor nerves. In the passage upwards through posterior pyramid consists of the posterior median column the medulla of the columns of the cord, a re-arrangement of the cord, and is prolonged through the pons to the of their fibres takes place ; just as in a great central railway cerebrum. The fasciculus teres is formed of a small part station, the rails, which enter it in one direction, intersect of the lateral column of the cord, and is also prolonged and are rearranged before they emerge from it in the opposite through the pons to the cerebrum.

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