118 HUMAN EMBRYOLOGY AND MORPHOLOGY. 



month. By the seventh month (Fig. 94) it is divided into two 

 parts, the cervix or lower segment and body or upper segment. 

 The lower segment or cervix forms then two-thirds of the uterus ; 

 its walls are thick and its upper part is lined by columnar non- 

 ciliated epithelium, containing mucous racemose glands. Its 

 mucous membrane is arranged in palmate folds. The upper or 

 uterine segment proper composes only a third of the uterus. It 

 is lined by columnar ciliated epithelium. Uterine glands are 

 developed in it after birth. At puberty the body of the uterus, 

 instead of being half the size of the foetal cervix, becomes larger 

 than it. The cervix takes no part in menstruation nor in con- 

 taining the foetus ; its true function is unknown. It is probably 

 glandular. 



THE PERINEUM. 



The Perineal Body (Figs. 94 and 95) is the triangular septum 

 of tissue which is developed in the perineum so as to separate the 

 rectum from the vagina. It contains the origin of the sphincters 

 of the anus and vagina, fat and fibrous tissue, and all the 

 structures between the recto-uterine fold of the peritoneum above 

 and the perineum below. 



In the male the corresponding part lies between the urethra 

 and the rectum. In man the perineal body is extremely large. 

 By its development the rectal part of the cloaca is separated from 

 that part of it which forms the uro-genital sinus (Fig. 95). The 

 perineal body is formed at the end of the 1st month of foetal 

 life in the following manner : 



The allantois grows out from the hind gut ; a prolongation of 

 the enteric cavity forms the canal of the allantois (Fig. 15, p. 96). 

 Hence in the 3rd week the hindermost part of the gut is common 

 to allantois and intestine, the common part forming the cloaca. 

 There is then no perineal body (Fig. 95 A). This is the permanent 

 condition in all vertebrates save the higher mammals — those higher 

 than the Monotremes. The Wolffian ducts open in the cloaca 

 near the neck of the allantois. A cleft appears on each side of 

 the cloaca, and the dorsal or rectal part is separated from the 

 ventral or uro-genital part. The ventral or uro-genital part of 

 the cloaca forms the bladder and uro-genital sinus, which are 



