112 



OBSTETRICAL FHYHIOLOG Y, 



the sexes become defined, and at this stage the organs may be studied 

 as internal and external. The indifferent stage begins about the sixth 

 week, when there appears on the lower face, and near the inner border 

 of the Wolffian body, a small white cord, which, in keeping this position, 

 increases in volume. This is the genital gland, which is fixed to the 

 body by folds of the serous membrane, and is composed of a collection 

 of young cells enclosed in an envelope. The development of this gland 

 is coincident with the formation of Mailer's duct or the genital canal, 

 which lies inside and in front of the Wolffian duct. Miiller's duct is at 

 first a solid cellular column, but is afterwards hollowed out into a 

 cavity ; it terminates in a cul-de-sac at its upper extremity, and opens 

 below into the bladder, near the Wolffian duct. From these modifica- 

 tions of the genital gland and the ducts of Miiller, it results that the 

 testicle arises from the gland, which shortens and widens a little, while 

 its tissue is transformed into the tubuU seminiferi. The head or globus 

 major of the epididymus, is formed by the middle portion of the Wolffian 

 body ; the tail or globus minor, the vas deferens, and the ejaculatory 



Fig. 60. 



Genito-ukinaey Organs of a Fcetal Sheep. 



a, a. Rudimentary Kidneys ; h, Ureters ; c, c, Testes ; d, d, Wolttian Bodies ; 

 e, e. Excretory Ducts of Wolffian Bodies or Sperm Ducts ; g, Oviduct with 

 its openings /, /. 



canal, are derived from the Wolffian duct. Lastly, the vesiculce semin- 

 ales and the commencement of the urethra are formed by the posterior 

 extremity of the ducts of Miiller, which joins the uro-genital sinus — the 

 very short canal communicating between the bladder and cloaca. The 

 developed testicle remains in the abdominal cavity, maintained there 

 by a peritoneal fold, the /j/z'ca gubernatrix ; or descends by the inguinal 

 canal into the scrotum. This descent is preceded by the appearance of 

 a preparatory structure — the gubernacidum testis — consisting of a central 

 axis of soft gelatinous substance containing many nucleated cells and 

 surrounded by fibrous tissue, which soon exhibits the striped character- 

 istics of voluntary muscle. Some of these fibres spring from the bottom 

 of the scrotum and traverse the abdominal ring, while others arise from 

 Poupart's ligament — the whole, enclosed by connective tissue and con- 

 nected by a fold of peritoneum to the psoas muscle, extending to the 

 testis. This gubernaculum, in shrinking or contracting, draws the 

 testis below the kidney to the abdominal ring, where it rests for a brief 

 space ; after which it reaches the scrotum, where it is found after birth 

 with the remains of the scrotal part cf the gubernaculum. The iliac 



