616 THE NERVOUS SYSTEM. 
of the ischio-rectal fossa and the fold of the nates behind the anus. This nerve 
replaces, in some cases, the perforating cutaneous nerve. 
Anterior Sacro-coccygeal Nerves (nn. ano-coccygei).—By the union of the 
remaining part of the fourth with the fifth sacral and coccygeal nerves, the 
so-called coccygeal plexus is formed. A fine descending branch of the fourth 
sacral nerve passes over or through the great sacro-sciatic ligament, to join the 
fifth sacral nerve. This fifth sacral nerve, joined by the descending branch of 
the fourth, descends alongside the coccyx and is again Joined by the coccygeal 
nerve, so that a plexiform cord results, homologous with the inferior caudal trunk 
of tailed animals. Fine twigs arise from it, which pierce the sacro-sciatic hgament 
and supply the skin in the neighbourhood of the coccyx, internal to the perforating 
cutaneous nerves and behind the anus. 
THE Pupic NERVE. 
The pudic nerve (n. pudendus) is the principal nerve for the supply of the 
perineum. It arises in the pelvis usually by three roots from the second, third, and 
fourth sacral nerves (Fig. 446, p. 614). (Frequently one of its branches, the inferior 
hemorrhoidal nerve, arises independently from the third and fourth sacral nerves.) 
2— __—Bulbo-cavernosus 
PERINEAL BRANCH OF SMALL 
SOLATIC a 
Mee Erector penis 
i es 
, = aS 
aN Transversus 
ANTERIOR SV 
—— perinel 
SUPERFICIAL 
PERINEAL a 
NERVE 
Ischial tuberosity 
POSTERIOR 
SUPERFICIAL 
PERINEAL  —__ 
NERVE 
_— Levator ani 
‘ae 
~ maximus 
GLUTEAL \ 
BRANCHES, \ 
OF SMALL—\ 
SCIATIC 
NERVE 
Parietal pelvic 
fascia 
Levator ani 
INFERIOR HAMORRHOIDAL 
NERVE External sphincter ani 
PERFORATING CUTANEOUS NERVE 
PERINEAL BRANCH OF FOURTH SACRAL NERVE ANTERIOR SACRO-COCCYGEAL NERVE 
Fic. 447.—THE MuscLes AND NERVES OF THE MALE PERINEUM. 
The nerve passes to the buttock through the great sacro-sciatic foramen below the 
great sciatic nerve, and lies on the lesser sacro-sciatic ligament, or the spine of the 
ischium, internal to the internal pudic artery. It enters the perineum along with 
the pudic artery through the small sacro-sciatic foramen. In the perineum it is 
deeply placed in the outer wall of the ischio-rectal fossa, enclosed in a special 
sheath derived from the parietal pelvic fascia covering the inner surface of the 
obturator internus muscle. At the anterior limit of the ischio-rectal fossa, the 
nerve approaches the surface and divides at the base of the triangular lhgament 
into its terminal branches, the perineal nerve and the dorsal nerve of the penis. 
The branches of the pudic nerve are essentially the same in the two sexes. 
As a rule no branches are given off till the nerve enters the perineum, but some- 
times the inferior hemorrhoidal nerve has an independent origin from the 
