GEKEEATIVE OEGANS OF VERTEBEATA. 



619 



in the former they are often broken up into several large lobes, 

 while in the latter they are distinguished by their length and by 

 the diverticula which are found on them. The terminal portion 

 also of the vas deferens often has a glandular structure. 



Besides the seminal ducts, the short terminal portion of which 

 receives the vesiculae seminales, and is known as the ductus ejacu- 

 latorius, rudiments of the Mullerian ducts open 

 into the urogenital sinus in many Mammals. 

 They either consist of a single or of a paired 

 diverticulum, which corresponds to a rudimentary 

 sinus genitalis of the female, or, rather, to its 

 vaginal portion, so that it is not very exact to 

 call it a uterus masculinus. Part of it some- 

 times forms a portion of the male genital sinus, for 

 the seminal ducts open into it. These organs are 

 largest in the Rodentia (Fig. 354, g), although, 

 indeed, they are not altogether wanting in other 

 forms ; in Man they are represented by the 

 prostatic vesicle. 



Lastly, the urogenital canal is provided with 

 yet another set of glandular organs, the prostatic 

 glands. These may be of a considerable size, 

 and form paired lobate structures (Rodentia, 

 Elephas, Insectivora) (Fig. 353, gl' gl"), or they 

 are formed of a number of smaller tubes, which 

 are connected by layers of smooth muscular 

 fibres to a mass which is attached to the wall 

 of the urogenital canal. By the further develop- 

 ment of the musculature, which is found on 

 these glands in other forms also, the prostate is 

 converted into a circular body. 



§ 456. 



rig. 354. Urogenital 

 canal and urinary 

 bladder of Lepus 

 Cnniculus. J. From 

 behind. B The 

 posterior wall of the 

 uterua masculinns is 

 laid open. C Side 

 view. V Bladder. 

 It, Ureter, d Seminal 

 dnct. g Sinus geni- 

 talis, ug Urogenital 

 canal. 



In the lower divisions the efferent ducts of 

 the ui'inary and generative apparatus unite with 

 the terminal portion of the enteric canal to open 

 into the cavity which has already (p. 562) been 

 called the " cloaca ; " but it is doubtful whether 

 this should be regarded as the primitive condition, 

 for we might take the arrangement which obtains 

 in the Cyclostomata, Ganoi'dei, and Teleostei, to 

 be such, where the urogenital organs and the tractus intestiaalis 

 open separately. In them, the anus is in front of the urogenital 

 orifices, although, and especially in the Ganoi'dei, there is a depres- 

 sion into which both these orifices open ; this depression is an early 

 indication of a cloaca. The cloaca is well developed in the Selachii, 

 and the orifices of the urogenital apparatus, which lie, in other forms, 

 behind the anus, are there placed on the dorsal wall of the cloaca. 



