NEUROLOGY. | 137 
wanting. The four superior, with the branch from the last lumbar, form 
the sacral plexus, placed on the sacrum behind the pelvic fasciz ; its form 
is somewhat triangular or palmate. ach of the sacral nerves, immediately 
after its emergence from the foramen, is joined by a short branch from one 
of the ganglions of the sympathetic. The sacral plexus sends off the follow- 
ing branches, both internally and externally : the internal or pelvic are the 
hemorrhoidal, vesical, and muscular, and in the female the uterine and the 
vaginal ; the external branches are the inferior or lesser sciatic, the inferior 
gluteal, posterior cutaneous, pudic, and great sciatic or posterior crural. All 
these escape by the lower part of the great sciatic notch below the pyriform 
muscle. The visceral branches arise from the fourth and fifth sacral, and are 
directed forwards into the cavity, there to be joined by numerous filaments 
from the sympathetic nerve, forming the hypogastric plexus, a complex net- 
work. of nervous filaments entangled around the branches of the internal 
iliac artery, and accompanying them to their terminations. 
The internal or pelvic muscular branches supply the levator ani, obturator 
internus, pyriformis, and sphincter ani. The lesser scvatec, inferior gluteal, 
and posterior cutaneous nerves, may all be regarded as one large, loose, and 
flat fasciculus, escaping from the pelvis below the pyriform muscle; branches 
are distributed to the perinzeal regions, and to the upper part of the leg. 
The pubic nerve arises from the third and fourth sacral, and, passing 
throngh the great sciatic notch or foramen, re-enters the pelvis by the lesser 
sciatic notch, and proceeds towards the pubes; it then divides into two 
branches, an inferior and a posterior. The inferior or perineal nerve, the 
larger of the two, is distributed to the muscles and integuments of the peri- 
neum. ‘The superior branch continues along the pubes to the symphyis, 
and is finally distributed to the subcutaneous cellular tissue of the glans 
penis. 
The great sciatic, or posterior crural nerve, is the principal branch of the 
ed plexus, and a largest nerve in the body. It proceeds from the four 
superior sacral nerves, forms a flat broad band, which escapes from the pel- 
vis below the pyriform muscle, and descends close to the outer side of the 
tuber ischii, along the back part of the thigh, as far as the ham, where it 
divides into the external and internal popliteal nerves, having given off 
numerous muscular and cutaneous branches.. About the middle of the 
thigh it often gives off a large nerve, the external articular, to the outer side 
of the knee joint. 
The external popliteal, or the peroneal nerve, is cen to supply the 
muscles on the external and anterior aspect of the leg, as also the integu- 
ments of the leg and dorsum of the foot. Descending, it gives off several 
long branches, termed the external cutaneous nerves of the leg ; one of these, 
‘the communicans peroncei, passes backwards over the outer part of the gas- 
trocnemius, and communicates with the external saphenous nerve. Passing 
round the joint.of the fibula, the peronzeal nerve divides into two branches, 
the. musculo-cutaneous and the anterior tibial. The musculo-cutaneous passes 
~~ down the leg, and a little above the external malleolus, divides into the 
internal and external tarsal nerves, or the dorsal nerves of the foot. The an- 
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