This area is divided into two lateral parts by a line drawn from the "central point of the perineum " to the tip of the coccyx, and the examining fingers may, in thin subjects, be made to sink deeply into each lateral recess (the ischio-rectal fossae), being then in relation with the rectum and levator ani muscle on the inner side, the ischial tuberosity and the obturator internus muscle on the outer side, the transverse perinei muscle in front, and the gluteus maximus and great sacro-sciatic ligament behind.
If the forefinger be gently inserted into the rectum, definite resistance is offered by the external and internal sphincters, the latter aided by contraction of the levator ani muscle. Further on the finger enters the dilated ampullary portion of the rectum, meeting, perhaps, further obstruction from Houston's valves. When insinuated as far as possible, the palmar aspect of the distal phalanx will, in the male, be in contact with the vasa deferentia and the vesiculae seminales, the middle phalanx with the prostate gland, and the proximal phalanx with the sphincters, which intervene between the finger and the triangular ligament and the spongy and membranous parts of the urethra. Posteriorly, the hollow of the sacrum and the coccyx can be fully explored. It is most important to bear in mind that the peritoneum is reflected from the rectum on to the upper third of the vagina in the female, and on to the vesiculae seminales, about 1 inch above the upper limit of the prostate gland, in the male.
In children, since the true pelvis is but little developed and the later pelvic viscera are practically abdominal, a rectal examination enables one to explore all the lower abdominal viscera, including the bladder.