THE LARGE INTESTINE 



1175 



toward the left, reaches the middle line and joins the rectum. It will lie, there- 

 fore, in more or less direct contact with the bladder (and uterus in the female), 

 and may possibly touch the caecum. It is very closely related with the coils of 

 small intestine that occupy the pelvis, and by these coils the loop is usually hid- 

 den. In about 90 per cent, of cases, the sigmoid colon lies entirely within the 

 true pelvic cavity. In the remainder, it loops upward for a variable distance 

 toward the umbilicus, a position normally found in infancy. 



Fig. 936. — Interior of the Rectum. ( X • .) (From Toldt's Atlas.) 

 Plica transversalis 



Sphincter ani 

 tertius 



Tunica mucosa 



Tunica [ Longitudi- 

 ™.>c,.„ nal layer 



Taris Circular 



'^"^ [ , layer 



Rectal columns 

 (Morgagnii) 



Rectal sinuses 



Sphincter ani externus 

 Sphincter ani internus 



Solitary lymph nodes 



Mucous folds 



Pars analis recti 



Annulus 

 hsemorrhoidalis 



Skin 



The sigmoid colon is attached to the abdominal and pelvic wall by the sigmoid mesocolon, 

 so that it is quite surrounded by peritoneum. The hne of attachment of this mesocolon is 

 as follows: It usually crosses the psoas in a slight curve upward so as to pass over the iliac vessels 

 at or about their bifurcation. The curve ends at a point either just to the medial side of the 

 psoas muscle, or between the psoas and the middle line, or, as is most frequently the case, just 

 over the bifurcation of the vessels. From this point the line of attachment proceeds vertically 



Fig. 937. — Mid-sagittal Section of the Male Pelvis. 



Bladder 



Symphysis pubis -^^ 



Urethral bulb 



(XI). (Braune. 



Recto-vesicaJ pouch 

 J Rectum 

 4-Transverse fold 

 „ .Vesicula seminalis 



Ductus ejaculatorius 



Prostate 



External sphincter ani 

 j- Internal sphincter ani 



External sphincter ani 



down, taking at first a slight curve to the right. Its course is to the left of the middle Une, 

 while its ending will be upon that line, about the second or third sacral vertebra. The sig- 

 moid mesocolon measures from 3 to 8.7 cm. in width — i. e., from the parietes to the bowel, — 

 at the widest point. 



When a descending mesocolon exists, it joins that of the sigmoid colon. There is often 

 no mesocolon over the psoas, the gut being adherent to that muscle. In connection with the 

 sigmoid mesocolon is often found a fossa or pouch of peritoneum, known as the inter sigvioid 

 fossa [recessus intersigmoideus]. This pouch is formed by the incomplete adhesion of the 



