878 A MANUAL OF ANATOMY 



and, after the rupture of the cloacal membrane in these animals, a common 

 outlet is formed by which intestinal or faecal matter, urine, and the products 

 of the genital organs escape. 



In Man the cloaca becomes partitioned off into two tubular compartments 

 by a fold, called the cloacal or uro-rectal septum. The two compartments 

 or canals are dorsal and ventral respectively. The dorsal canal gives rise to 

 (i) the rectum, and (2) the upper two-thirds of the anal canal, or the part 

 above the anal valves. The ventral canal leads caudalwards from the opening 

 of the allantoic diverticulum, and is called the uro-genital sinus or canal. The 

 allantoic diverticulum and the uro-genital ducts open into it. 



The recto-anal and uro-genital canals are directed towards the cloacal 

 membrane, which closes both of them ventrally and caudalwards. The 

 uro-rectal septum is connected inferiorly with the cloacal membrane, and 

 this membrane is divided into two parts — namely, dorsal or anal, known as 

 the anal membrane, and ventral or uro-genital. 



The anal and uro-genital parts of the cloacal membrane are separated extern- 

 ally by a transverse fold, known as the pre-anal, ano-gential, or perineal fold. 

 This fold undergoes considerable thickening, and gives rise to the perineal body. 



The anal membrane soon becomes invaginated, and a superficial pit is 

 thereby produced, called the anal depression or proctodseum. The depression 

 consists of invaginated ectoderm which meets the intestinal entoderm, and the 

 two layers construct the anal membrane, or anal part of the cloacal mem- 

 brane. The condition of matters may be compared to the invagination of 

 ectoderm, which forms the primitive oral cavity or stomodaeum, and which, 

 meeting with the entoderm of the pharyngeal part of the fore-gut, forms the 

 bucco-pharjmgeal membrane. 



About the beginning of the fourth month the cloacal membrane (anal 

 and uro-genital) ruptures and disappears. The rupture of the anal part of 

 the cloacal membrane gives rise to an aperture called the anus, through 

 which the hind-gut and proctodaeum become continuous. The lower one-third 

 of the anal canal — that is to say, the limited portion below the anal valves — is 

 formed by the ectoderm of the anal fossa or proctodaeum. 



In some cases the anal membrane — namely, that part of the cloacal mem- 

 brane which separates the hind-gut from the anal fossa or proctodaeum — is 

 persistent. Such a condition is known as atresia ani or imperforate anus. 



The uro-genital part of the cloacal membrane becomes depressed, and so 

 gives rise to the uro-genital fossa. When this part of the membrane ruptures, 

 the uro-genital opening or cleft is formed, by which the uro-genital compartment 

 of the cloaca — namely, the uro-genital sinus or canal — communicates with 

 the exterior. 



The Female Pelvis. 



The female pelvis contains the pelvic colon and rectum, with 

 a few coils of the small intestine ; the bladder and urethra ; the 

 uterus and vagina ; and the uterine appendages connected with 

 the broad ligaments, namely, the Fallopian tubes, the ovaries, with 

 the parovarium or epoophoron, and paroophoron (the latter in early 

 life) ; and the round ligaments of the uterus. The arteries are the 

 same as in the male, with the addition of portions of the ovarian 

 arteries, and the uterine arteries, and the substitution of the 

 vaginal arteries for the inferior vesical arteries in the male. The 

 venous plexuses are hemorrhoidal, vesical, pudendal, ovarian, 

 uterine, and vaginal. The nerve-plexuses peculiar to the female 

 are the uterine, ovarian, and vaginal. 



General Position of the Viscera. — The pelvic colon and rectum 

 are situated as in the male pelvis. The bladder lies anteriorly, 

 being situated immediately behind the bodies of the pubic bones, 



