THE SACRAL PLEXUS. 793 



The femoral cutaneous branches (descending) are numerous filaments, derived 

 from both sides of the nerves, which are distributed to the back, inner, and outer 

 sides of the thigh, to the skin covering the popliteal space, and to the upper part 

 of the leg. 



The Perforating Cutaneous Nerve usually arises from the second and third sacral 

 nerves, and is of small size. It is continued backward through the great sacro- 

 sciatic ligament, and, winding round the lower border of the Gluteus maximus, 

 supplies the integument covering the inner and lower part of that muscle. 



The Pudic Nerve is the direct continuation of the lower cord of the sacral 

 plexus, and derives its fibres from the third and fourth sacral nerves, and frequently 

 from the second also. It 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 

 upward and forward along the outer wall of the ischio-rectal fossa, being contained 

 in a sheath of the obturator fascia, termed Alcock's canal, and divides into two 

 terminal branches, the perineal nerve and the dorsal nerve of the penis or clitoris. 

 Before its division it gives off the inferior hemorrhoidal nerve. 



The inferior hemorrhoidal nerve is occasionally derived separately from the 

 sacral plexus. It passes across the ischio-rectal fossa, with its accompanying 

 vessels, toward the lower end of the rectum, and is distributed to the Sphincter 

 ani externus and to the integument round the anus. Branches of this nerve com- 

 municate with the inferior pudendal and superficial perineal nerves at the fore part 

 of the perineum. 



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

 pudic, is situated below the pudic 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 or external branch pierces the base of the triangular 

 ligament of the urethra, and passes forward along the outer side of the urethral 

 triangle in company with the superficial perineal artery ; it is distributed to the 

 skin of the scrotum. It communicates with the inferior hemorrhoidal, the inferior 

 pudendal, and the other superficial perineal nerve. The anterior or internal branch 

 also pierces the base of the triangular ligament, and passes forward nearer to the 

 middle line, to be distributed to the inner and back part of the scrotum. Both 

 these nerves supply the labia rnajora in the female. 



The muscular branches are distributed to the Transversus perinsei, Accelerator 

 urinae, Erector penis, and Compressor urethrae. A distinct branch is given off 

 from the nerve to the Accelerator urinse, which pierces this muscle, and supplies 

 the corpus spongiosum, ending in the mucous membrane of the urethra. This 

 is the nerve to the bulb. 



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

 accompanies the pudic artery along the ramus of the ischium ; it then runs forward 

 along the inner margin of the ramus of the os pubis, between the superficial and 

 deep layers of the triangular ligament. Piercing the superficial layer it gives a 

 branch to the corpus cavernosum, and passes forward, in company with the dorsal 

 artery of the penis, between the layers of the suspensory ligament, on to the dorsum 

 of the penis, along which it is carried as far as the glans, to which it is distributed. 



In the female the dorsal nerve is very small, and supplies the clitoris. 



The Great sciatic nerve (Fig. 423) supplies nearly the whole of the integument 

 of the leg, the muscles of the back of the thigh, and those of the leg and foot. It 

 is the largest nervous cord in the body, measuring three-quarters of an inch in 

 breadth, and is the continuation of the upper division of the sacral plexus. It 

 passes out of the pelvis through the great sacro-sciatic foramen, below the Pyri- 

 formis muscle. It descends between the trochanter major and tuberosity of the 

 ischium, along the back part of the thigh, to about its lower third, where it divides 

 into two large branches, the internal and external popliteal nerves. 



This division may take place at any point between the sacral plexus and the 



