THE FCETUS. 923 



the development of the genital organs ; the other gives rise to organs whose 

 signification is unknown such as the organ of Eosenmiiller, which is very 

 developed in the Mare, and the canals of Gaertner, visible in the Cow (Mare, 

 and Pig). 



A. URINARY ORGANS. We have seen above how the allantois is derived 

 from the terminal portion of the intestine ; it has now to be stated that the 

 bladder is derived from the allantois. This reservoir is the result of the 

 dilatation of the abdominal portion of the allantois. During foetal life, the 

 bladder is extended by the urachus to the umbilical ring ; but after birth 

 the urachus is obliterated, and the bladder is withdrawn into the pelvic 

 cavity. Hereafter we shall study the urethra. 



The kidneys appear a long time after the Wolffian bodies, in the shape of 

 two blind pouches constituted by a pushing back of the upper wall of the 

 small vesicle of the allantois. These little culs-de-sac ramify, and are 

 afterwards replaced by solid buds, in whose interior are developed the 

 uriniferous canals and Malpighian bodies. According to certain observers, 

 the kidneys subsequently communicate with the ureters, which are developed 

 separately in the middle layer of the blastoderm. 



(In the female, the Wolffian bodies do not entirely disappear ; the 

 canals of Gaertner and the bodies of Eosenmiiller, situated in the broad 

 ligaments, between the ovaries and Fallopian tubes, are their remains in 

 adult life ; traces of them are also found in the male, near the head of the 

 epididymis, where they constitute the vas aberrans of the testicles. The 

 suprarenal capsules are very large in the Equine foetus, being nearly one 

 half the size of the kidneys.) 



B. GENITAL ORGANS. The genital apparatus of the male and female are 

 at first very much alike ; indeed, during a certain period it is impossible to 

 distinguish the sexes ; so that some authorities have proposed to term this 

 period the " indifferent state of the genital organs." Later, the sexes are 

 defined ; and this period of development may be studied in the internal and 

 external organs. 



1. Indifferent state of the internal genital organs. Towards the sixth 

 week, there is observed on the lower face, and near the inner border of the 

 Wolffian bodies, a little white cord, which increases in volume and maintains 

 almost the same position. This is the genital gland, which is attached to 

 the Wolffian body by serous folds, and is formed by a mass of young cells 

 sustained by an enveloping membrane. 



The development of this gland is accompanied by the formation of the 

 genital or Mutter's duct, which is seen to the inside, and in front of, the 

 Wolffian duct. Miiller's duct is at first a solid cellular column, which 

 afterwards becomes a canal; it terminates above in a blind pouch, and 

 opens, below, into the bladder, near the Wolffian duct. 



Development of the internal genital organs of the male. These result from 

 modifications of the genital gland and Miiller's duct. The testicle arises 

 from the gland, which shortens and widens a little, while its tissue is 

 transformed into seminiferous canaliculi. The head (globus major) of the 

 epididymis is formed by the middle portion of the Wolffian body ; the tail 

 (or globus minor), vas deferens, and ejaculatory duct, are derived from the 

 Wolffian duct. Lastly, the vesiculce seminales and the origin of the urethra 

 are formed by the posterior extremity of Miiller's ducts, which join and 

 open into the uro-genital sinus, as the very short canal is named which 

 communicates between the bladder and cloaca. The developed testicle 

 remains in the abdominal cavity, or descends through the inguinal canal 



