388 



EMBRYOLOGY. 



which has come into communication with the seminal tubules by 

 means of individual canals, in the manner previously described, and 

 has thereby furnished the rete testis and the tubuli recti, is converted^ 

 into the bead of the opididymis. It exhibits in the tenth to the 

 twelfth week from ten to twenty short transverse canals, which are 

 now to be designated as vasa efferentia testis. They unite in the 

 mesonephric duct (fig. 222), which continues to have a straight 

 course, and has now become the seminal duct (si, vas defer ens). 

 During the fourth and fifth months the individual canals begin to 

 grow in length and thereby to become tortuous. The vasa efferentia 



in this way produce the coni vasculosi, 

 which are at once the initial part of 

 the vas deferens and the tail of the 

 epididymis. 



Incidentally let it be stated that near the 

 external opening of the vas deferens, as it 

 passes along the posterior surface of the 

 bladder, there arises in the third month a 

 small evagination, which becomes the seminal 

 vesicle (sbl). 



The posterior region of the primitive 

 kidney (pa) degenerates into very in- 

 significant remnants. In older embryos 

 one still finds for a time, between vas 

 deferens and testis, small, tortuous 

 canals, usually blind at both ends, be- 

 tween which degenerated Malpighian 

 corpuscles also occur. The whole forms 

 a small yellow body. In the adult these 



remnants are still further reduced ; they produce on the one hand 

 the vasa aberrantia of the epididymis, and on the other the organ 

 discovered by GIRALDES, the paradidymis. The latter consists, 

 According to HENLE'S description, of a small number of flat, white 

 bodies, lying in contact with the blood-vessels of the seminal cord, 

 each of which is a knotted tubule blind at both ends ; each tubule is 

 lined with an epithelium containing fat, and is enlarged at its blind 

 ends into irregularly lobed vesicles. 



The Miillerian ducts (fig. 222 mg) do not acquire in the male any 

 function, and therefore, as useless structures, undergo <l<'Lr''nerati<>n ; 

 the middle region in fact usually disappears without leaving a trace 

 although it has been for a time during embryonic life demonstrable as 



Fig. 221. The internal sexual organs 

 of a male human embryo 9 cm. 

 long, after WALDEYER. Magnified 

 8 diameters. 



A, Testis ; nh, epididymis (sexuaJ part 

 of the primitive kidney) ; pa, 

 paradidymis (remnant of the 

 primitive kidney); si, vas deferens 

 (duct of the primitive kidney); 

 a, vascular bundle of connective 

 tissue. 



