Anatomy and Physiology 



In origin and early development the ovary and testis are identi- 

 cal. The gonad and mesonephros or primitive kidney are de- 

 veloped from the urogenital fold. The gonad first forms as a 

 medio-ventral thickening of the fold, which gradually expands 

 until it becomes attached by a mere stalk. At first, the gland is 

 made up merely of a superficial epithelial layer, and an inner 

 epithelial mass, or epithelial nucleus. In the process of develop- 

 ment, large primordial germ cells migrate from the entoderm of 

 the future intestinal canal, and pass through the stalk to the gonad. 

 In the case of the male gonad, seminiferous tubules are very 

 difficult to make out in eml)ryos smaller than 24 millimeters. Then 

 they suddenly differentiate out as solid cords of germ cells, -while 

 the connective tissue grows in around them. These connective 

 tissue sheaths unite at the center of the organ to form the anlage 

 of the mediastinum testis. The testicular tubules unite and con- 

 verge toward the hilus, there to meet the anlage of the rete. At 

 the mesonephric end of the testis, the rete first appears as a col- 

 lection of cells, differentiating out from the inner epithelial mass 

 of the gonad. These cells gradually grow out to meet the collect- 

 ing portions of the mesonephric tubules on the one hand, and the 

 seminiferous tubules on the other. The rete is represented as 

 cords of cells at first, which in forty millimeter embryos hollow out 

 to form tubules. 



The mesonephros, or primitive kidney, ea;'ly starts to degenerate 

 cranio-caudally, — the tubules becoming separated into a cranial 

 and caudal group. The collecting and secretory parts of the 

 cranial group separate, the collecting tubules growing out to meet 

 the rete with wliieh they unite to form the efferent ductules of the 

 epididymis. The caudal group of tubules is vestigial and becomes 

 the paradidymis. The mesonephric duct becomes the vas deferens, 

 connecting as it does with the tubules of the epididymis, and 

 emptying into the urethra at Mliller's tubercle or, as it later be- 

 comes, the colliculus seminalis. 



The seminal vesicles arise as hollow saccules from the dorsal 

 wall of the mesonephric duct just as it empties into the urethra. 

 The prostate develops aa an outgrowth of the dorsal urethra .just 

 posterior to ]\[iiller's tubercle. The bulbo-urethral glands appear 

 as solid, paired, epithelial outgrowths from the entoderm of the 

 urogenital sinus. 



!Miiller's duct, at first a solid tube growing from the anterior 

 part of the mesonepliros, and ending at ^Midler's tubercle, becomes 

 a hollow tube, and in the female forms the entire genital tract ex- 

 cept for the gonad and the lower part of the vagina. In the male, 

 the anterior part remains as the vestigial appendix testis, and the 

 posterior part, as the vagina masculina, Ellenberger states, how- 

 ever, that this embryonic structure is very seldom seen in the 

 mature bull. 



