Prepared in this manner, the perineum pre sents anteriorly a well-marked median promi nence corresponding to the urethra, and which for obvious reasons enlarges considerably in the living subject during erection. At either side of this urethral prominence a parallel de pression exists, external to which the resisting edges of the mmi of the ischium and pubis may be always readily recognised by the finger. At the posterior part of the perineum the point of the coccyx may be felt distinctly in the middle line ; the tuberosities of the ischia covered by a great depth of soft parts project remarkably at the sides, constituting the extreme lateral limits of the region, whilst the mid space between these eminences exhibits a deep depression containing the anus. In front of the anus a central elevation of the skin termed the rapho extends forwards along the perineum, and may be traced distinctly to the scrotum and penis; it serves as a guide to the surgeon in many operations, pointing out the rniddle line accu rately so long as the integuments retain the' normal relations.
Integument. —The characters of the cut. neous covering of the perineum are not unifo throughout ; in some situations its thickness i very considemble, whilst in others it app remarkably delicate. In front the skin becom gradually finer as it approaches the scrotum and at the margins of the anus its delicacy i extreme ; but in the neighbourhood of th tuber ischii arid along the edge of the glute maximus it possesses great density and offe considerable resistance to the scalpel : at th circumference of the region it in fact gmduall assumes the properties of the neighbouring t gumentary membrane, resembling that of the scrotum anteriorly, merging insensibly into the integument of the buttock arid thigh laterally, and even approaching to the characters of mu cous membrane in the vicinity of the gut ; it is generally of a dark brown colour in the healthy adult, and of a lighter hue in the child ; but there are in this respect numerous individual varieties ; the darker the teint the more highly developed usually are the subjacent muscles. Cutaneous follicles abound in the perineum and occur in greatest numbers near the anus and at the root of the scrotum, where their secre tions are most required. The skin around the anus is thrown into rugs disposed in a radiated manner, and which produce a puckered appear ance so long as the orifice remains contracted : they disappear during its dilatation, and are de signed to favour the extreme distension to which the anal extremity of the intestine is occasion ally subjected during defmcation. The folds in
question become at times the seat of fissure, ulceration, or excrescence, which may demand surgical interference for their relief.
In the lateral opemtion of lithotomy the first incision should commence at the left side of the raphe, about an inch or an inch and a quarter in front of the anus, and extend in an oblique direction backwards and outwards to the point midway between the tuber ischii and the orifice of the gut. In the bilateral operation the first incision is semilunar, the cornua placed at either side between the tuber ischii and the anus, and equidistant from these points respec tively, the centre situated about three quarters of an inch in front of the anal aperture, and the concavity of the curve directed backwards. For convenience the operator in general begins this incision on the right side of the perineum.
On removing the integuments the anatomist briar's into view anteriorly the superficial fascia of the perineum, surrounding the anus the cuta neous sphincter, and at either side of the gut a large quantity of adipose cellular tissue, which fills up in great measure the interval between the intestine and the tuber ischii. If the dis section have been carefully conducted, some ner vous twigs are also visible near the rami of the ischium and pubis ; they are mostly cutaneous and derived from the sciatic branch of the lesser sciatic nerve (the " perineal cutaneous " of many authors, the " long inferior pudendal " of Semmering) in its course to the scrotum and root of the penis. This nerve or its branches are always superficial and liable to injury in many operations performed upon the perineum.
The superficial fascia.—The superficial peri neal fascia has Leen by some anatomists de scribed as two membranes essentially separate and distinct from each other, that nearer to the surface being called the " subcutaneous cellular membrane" of the region, and the deeper of the two being designated " the superficial fascia of the perineum." To the writer this description appears unnecessarily minute, for in fat subjects it is exceedingly difficult to effect such a sepa ration, and under the most favourable circum stances the dissection in question is too artificial; with equal propriety might the superficial fascia of the abdomen be divided into layers, for like that in the perineurn, its cutaneous surface is cellular and often loaded with fat, whilst its deeper surface assumes very much an aponeu rotic appearance.