I04 



OBSTETRICAL PHYSIOLOGY. 



the small vesicle of the allantois. These small cavities become ramified, 

 and are ultimately replaced by solid tubercles, in whose interior are 

 developed the tubuli uriniferi and the Malpighian tufts. According to 

 some observers, the kidneys only subsequently communicate with the 

 ureters, which are developed separately in the middle lamina of the blas- 

 toderm, and terminate in the pelvic portion of the allantois. 



The genital organs of the male -xr^d. female offer, at the commencement 

 of their development, the greatest analogies. For a certain time it is 

 impossible to distinguish the sexes ; so that some authorities propose to 

 term this the " indifferent " state of the genital organs. Afterwards 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, in- 

 creases in volume. This is iht 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 Muller's duet 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 modifications 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 



Genitourinary Organs of a Fcetal Sheep. 



a, a, Rudimentary Kidneys ; b, Ureters ; c, c, Testes ; d, d. Wolffian Bodies ; e, c, Excretory 

 Ducts of Wolffian Bodies or Sperm Ducts ; ^, Oviduct with its openings/",,/ 



into the tubuli 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 canal, are derived from the 

 Wolffian duct. Lastly, the vesiculce seminales and the commcjtcement of the 

 urethra are formed by the posterior extremity of the ducts of Miiller, 

 which joins the urogenital sinus — the very short canal communicating 

 between the bladder and the cloaca. The developed testicle remains in 

 the abdominal cavity, maintained there by a peritoneal fold, the plica 

 gubernatrix ; or descends by the inguinal canal into the scrotum. This 

 descent is preceded by the appearance of a preparatory structure — the 

 gubernaculum testis — consisting of a central axis of soft gelatinous sub- 

 stance containing many nucleated cells and surrounded by fibrous tissue, 

 which soon exhibits the striped characteristics of voluntary muscle. 

 Some of these fibres spring from the bottom of the scrotum and traverse 



