THE RECTUM. 1037 
The rectum beeins at the termination of the pelvic mesoeolon, namely, about the 
fo} ) » he) 
level of the third sacral vertebra, and ends, where the bowel pierces the pelvic floor, 
opposite the lower and back part of the prostate in the male, or at a point 1} inches 
(3°7 cm.) in front of, but at a lower level than, the tip ef the coccyx in both sexes. 
It first descends along the front of the sacrum and coccyx, following the curve of 
these bones; beyond the coecyx, it rests, for about 14 inches (5-7 cm.), on the back 
part of the pelvic floor, here formed by the union of the two levatores ani; and 
finally, having reached the lower part of the prostate, it bends rather abruptly 
backwards and downwards, and, piercing the pelvic floor, passes into the anal 
canal (Fig. 704). __ 
Its general direction is downwards, but this varies at its two extremities, being 
downwards and backwards above, downwards and strongly forwards below. 
Curvatures.—The rectum is far from straight, notwithstanding its name, 
Posterior superior spine—— 
Third sacral vertebra 
Upper lateral inflexion a 
Fourth sacral vertebra 
(cut) 
: Lower border of 
Peritonewn (pararectal te riformis (cut 
fossa) pyriforiis (cut) 
Superior hemorrhoidal 
e B a artery 
Superior hemorrhoidal : J 
artery 
Lateral inflexion 
Rectum 
Coccygeus 
Great sciatic ligament—— 
Ischio-rectal fossa 
Anal canal — r External sphincter 
Anus 
Fic. 701.—-THE RECTUM FROM BEHIND. 
The sacrum has been sawn across through the 4th sacral vertebra, and its lower part removed with the coccyx. 
The posterior portions of the coccygei, levatores ani, and of the external sphincter have been cut away. 
The “ pinching in” of the lower end of the rectum by the inner edges of the levatores ani, resulting in the 
formation of the flattened anal canal, is suggested in the illustration, which has been made from a 
formalin-hardened male body, aged thirty. The lateral inflexions of the rectum, corresponding to 
Houston's valves, are also shown. 
which describes its condition fairly accurately in most animals, but not in man, in 
whom it is curved in both the antero-posterior and the transverse planes. 
Viewed from the side (Fig. 737), 1t forms a gentle curve, with the convexity 
backwards, which extends from the beginning of the rectum to the back of the 
prostate, and fits into the hollow of the sacrum and coccyx. At the back of the 
prostate a second curve is formed where the rectum joins the anal canal; this 
has its convexity directed forwards, whilst its concavity embraces the ano-coccygeal 
body—the mass of muscular and connective tissue which les between the tip of 
the coccyx and the anal canal. 
