THE EXTERNAL ORGANS. 127 



they usually enter by the end of the eighth month. But previously to this, a pouch 

 of peritoneum the processus vaginalis has descended into the scrotum along the 

 abdominal ring, pushing before it part of the internal oblique muscle and the 

 aponeurosis of the external oblique, which form respectively the cremasteric muscle 



Fig. 154. DIAGRAMS TO ILLUSTRATE THE DESCENT OP THE TESTICLE AND THE FORMATION OF ITS 



COVERINGS. (0. Hertwig.) 



In A the testicle is lying close to the internal abdominal ring. In B it has passed into the sac of 

 the tunica vaginalis. 1, skin of abdomen ; 1', skin of scrotum ; 2, superficial abdominal fascia ; 2', 

 Cooper's fascia ; 3, muscular and aponeurotic layer of abdominal wall ; 3', cremaster muscle and sper- 

 matic fascia ; 4, peritoneum ; 4', processus vagiualis ; 4" visceral layer of processus vaginalis covering 

 testicle ; t, testicle ; v.d., vas deferens ; r, internal abdominal ring. 



and spermatic fascia (fig. 154). This pouch, after the descent of the testicle into 

 it, becomes shut off from the abdominal cavity, and forms the cavity of the tunica 

 vaginalis. The descent of the testicle into the scrotum is intimately connected with 

 changes in the gubernaculum. The gubernaculum extends, as before mentioned, 

 from the integument of the groin, which afterwards forms the scrotum, upwards 

 through the abdominal ring to the lower part of the epididymis. When the pro- 

 cessus vaginalis is formed, the gubernaculum lies behind the serous sac. The 

 descent of the testicle is accompanied by a shortening of the gubernacular cord, 

 which thus appears to draw the organ downwards into the scrotum, and the testicle 

 following the line originally taken by the gubernacular cord, also passes down along 

 the posterior wall of the processus vaginalis, which it therefore invaginates from 

 behind. 



In many animals the testicles remain throughout life in the abdominal cavity. In others 

 they only descend into the scrotum during the period of " heat." Cases of cryptorchismus, in 

 which one or both testicles have failed to reach the scrotum, and have remained either in the 

 inguinal canal or within the abdominal cavity, are not unfrequent in the human subject. 



The ovaries also undergo a considerable change of position, accompanied by a 

 shortening of the band which corresponds with the gubernaculum testis in the male. 

 This band, as it passes by the united part of the Miillerian ducts which are forming 

 the body of the uterus, becomes attached laterally to that organ, and the descent of 

 the ovary is normally arrested at the side of the uterus. In rare cases, however, the 

 ovaries pass through the abdominal ring by the canal of Nuck, and may even be 

 found in the labia majora, where they resemble in position the testicles within the 

 scrotum. 



The External Organs. The external organs are up to a certain time entirely 

 of the same form in both sexes, and the several organs which afterwards distinguish 

 the male and female externally have a common origin (see fig. 155). A cloaca exists 

 till after the fifth week, and the genital eminence from which the clitoris or penis is 

 formed makes its appearance in the course of the fifth or sixth week in front of and 

 within the orifice of the cloaca. In the course of the seventh and eighth weeks this 

 orifice is seen to be divided into two parts ; but the exact manner in which the sepa- 

 ration of the two apertures takes place has not been accurately traced. The process 



