a 
1232 SURFACE AND SURGICAL ANATOMY. 
bounded by the levator ani and coccygeal muscles covered by the anal fascia ; 
the outer wall by the obturator internus muscle covered by the obturator fascia. 
An abscess in the ischio-rectal fossa should be opened early, otherwise it is liable — 
to burst through the inner wall into the rectum; should it open also upon the 
skin surface a complete “ fistula in ano” is formed. When a “ fistula in ano” results 
from the bursting of a submucous abscess of the anal canal the track of the fistula 
runs either internal to or through the fibres of the internal and external sphincter 
muscles, and the external or skin opening is, as a rule, close to the anus, while the 
internal opening is generally within the upper end of the anal canal. Occasionally 
the ischio-rectal abscess perforates the levator ami towards the apex of the fossa ; 
it then burrows into the peri-rectal cellular tissue of the pelvis, and opens into the » 
ampulla of the reetum. In other cases, again, the abscess starts in the peri-rectal 
tissue internal to the levator ani, and either bursts into the rectal ampulla or 
through the levator ani into the ischio-rectal fossa, and so reaches the surface. Or 
the pus may burrow between the rectum and coccyx, whence it may pass outwards 
through the great sacro-sciatic foramen behind the parietal pelvic fascia into the 
buttock ; or, by piercing the visceral layer of the pelvic fascia, may reach the extra- 
peritoneal fatty tissue of the pelvis and ascend in it to form an iliac abscess. 
The / ymphaties from the anus pass along the perimeo-crural folds to the inner- 
most glands of the groin, both inguinal and crural. From the rectum the majority 
of the lymphatics pass through a chain of glands which lie alongside the superior 
hemorrhoidal vessels in the retro-rectal cellular tissue in front of the sacrum ; — 
others, accompanying the middle heemorrhoidal ves, go to the glands in the 
neighbourhood of the internal iliac vessels. 
In making a rectal exramination the finger should be carried forwards from the tip of — 
the coceyx so as to enter the anus from behind. ‘The finger is then gently pressed upwards | 
and slightly forwards through the sphincteric region in the axis of the anal canal until it 
reaches the cavity of the rectum, the lower part of which is dilated to form the ampulla. 
The folds or valves of Houston, three in number, project into the cavity of the bowel in 
the form of prominent crescentic shelves, which are produced by the three permanent or 
true flexures into which the rectum is thrown (Birmingham) ; the lower valve, which may 
be suthciently prominent to impede the passage of the finger, must not be mistaken for a 
pathological condition. Through the anterior wall the finger can palpate from below up- 
wards the bulb of the urethra, the membranous parts of the urethra, Cowper’s glands (when 
inflamed and enlarged), the apex and lateral lobes of the prostate, the vesiculie seminales 
(when diseased), and the external trigone of the bladder. With the left forefinger in the 
rectum, an instrument passed into the bladder can be distinctly felt as it traverses the mem- 
branous urethra ; as it lies in the prostatic urethra it is separated from the finger by the pro- 
state. Hence, when a false passage is made through the bulbous or membranous portion of 
the urethra, the instrument, if pushed onwards towards the bladder, will be felt immediately — 
outside the rectum between it and the prostate. In the child, owing to the rudimentary 
condition of the prostate, the instrument is distinctly felt close to the rectum, as it lies in 
the prostatic as well as in the membranous portion of the urethra. When the prostate is 
not enlarged the tip of the finger can just reach the external trigone, which is most dis- 
tinetly felt when the bladder is full. The vesicule seminales, indistinctly felt when 
healthy, may be readily palpated when enlarged and indurated from disease. Through 
the lateral wall of the rectum m: Ly be palpated the ischio-rectal fossa, the bony wall of the 
true pelvis, and, when enlarged, the internal iliac lymphatic glands; through the posterior 
wall the hollow of the sacrum and coceyx, and the lymphatic glands lying in the retro- 
rectal cellular tissue. 
In the child rectal examination enables one to palpate, in addition to the structures i 
the cavity of the true pelvis, those which occupy the lower segment of the abdomen. 
When the bladder is empty even a small calculus can be readily felt by recto-abdominal 
palpation. 
The distance of the apex of the recto-vesical pouch of peritoneum from the anus 
varies considerably, according to the degree of distension of the bladder and rectum ; 
when both are empty it reaches to about 2 in. from the anus; when both are 
distended it is at least one imch higher. As pointed out by Birmingham, the 
peritoneum is closely adherent to the rectum above and in front, while at the side 
and below the connexion is much looser, so that by stripping the peritoneum 
