SACRAL PLEXUS. 657 



sciatic foramen to the inner surface of the Obturator Internus ; the branch to 

 the Gemellus Superior arises from the lower part of the plexus, near the pudic 

 nerve ; the small branch to the Gemellus Inferior and Quadratus Femoris also 

 arises from the lower part of the plexus; it passes beneath the Gemelli and 

 tendon of the Obturator Internus, and supplies an articular branch to the hip- 

 joint. This branch is occasionally derived from the upper part of the great 

 sciatic nerve. 



The Superior Gluteal Nerve (Fig. 358) arises from the back part of the lumbo- 

 sacral ; it passes from the pelvis through the great sacro-sciatic foramen above 

 the Pyriformis muscle, accompanied by the gluteal vessels, and divides into a 

 superior and an inferior branch. 



The superior branch follows the line of -origin of the Gluteus Minimus, and 

 supplies it and the Gluteus Medius. 



The inferior branch crosses obliquely between the Gluteus Minimus and Glu- 

 teus Medius, distributing filaments to both these muscles, and terminates in the 

 Tensor Vaginae Fernoris, extending nearly to its lower end. 



The Pudic Nerve arises from the lower part of the sacral plexus, and leaves 

 the pelvis, through the great sacro-sciatic foramen, below the Pyriformis. It 

 then crosses the spine of the ischium, and re-enters the pelvis through the 

 lesser sacro-sciatic foramen. ' It accompanies the pudic vessels upwards and for- 

 Avards, along the outer wall of the ischio-rectal fossa, being covered by the 

 obturator fascia, and divides into two terminal branches, the perineal nerve, 

 and the dorsal nerve of the penis. Near its origin, it gives off the inferior 

 hsemorrhoidal nerve. 



The inferior hsemorrhoidal nerve is occasionally derived from the sacral plexus. 

 It passes across the ischio-rectal fossa, with its accompanying vessels, towards 

 the lower end of the rectum, and is distributed to the External Sphincter and 

 the integument round the anus. Branches of this nerve communicate with the 

 inferior pudendal and superficial perineal nerves on the inner margin of the thigh. 



The perineal nerve, the inferior and larger of the two terminal branches of 

 the pudic, is situated below the pudio artery. It accompanies the superficial 

 perineal artery in the perineum, dividing into cutaneous and muscular branches. 



The cutaneous branches (superficial perineal) are two in number, posterior 

 and anterior. The posterior branch passes to the back part of the ischio-rectal 

 fossa, distributing filaments to the Sphincter Ani and integument in front of 

 the anus, which communicate with the inferior haemorrhoidal nerve; it then 

 passes forwards, with the anterior branch, to the back of the scrotum, communi- 

 cating with the anterior branch and with the inferior pudendal. The anterior 

 branch passes to the fore part of the ischio-rectal fossa, in front of the preceding, 

 and accompanies it to the scrotum and under part of the penis. This branch 

 gives one or two filaments to the Levator Ani. 



The muscular branches are distributed to the Transversus Perinei, Accele- 

 rator Urina3, Erector Penis, and Compressor Urethrae. The nerve of the bulb 

 supplies the corpus spongiosum ; some of its filaments run for some distance 

 on the surface, before penetrating to the interior. 



The dorsal nerve of the penis is the superior division of the pudic nerve ; it 

 accompanies the pudic artery along the ramus of the ischium, and between the 

 two layers of the deep perineal fascia ; it then pierces the suspensory ligament 

 of the penis, and accompanies the arteria dorsalis penis to the glans, to which 

 it is distributed. On the penis, this nerve gives off a cutaneous branch, which 

 runs along the side of the organ ; it is joined with branches of the sympathetic, 

 and supplies the integument of the upper surface and sides of the penis and 

 prepuce, giving a large branch to the corpus cavernosum. 



In the female, the pudic nerve is distributed to the parts analogous to those 

 in the male; its superior division terminating in the clitoris, its inferior in the 

 external labia and perineum. 



The Small Sciatic Nerve (Fig. 358) supplies the integument of the perineum 



