834 MAMMALIA. 



(2472.) The third portion of the urethra is enclosed in the body of 

 the penis, and surrounded by the erectile tissue, of which that organ 

 essentially consists ; but in all quadrupeds this part of the canal is not 

 so decidedly continuous with the muscular portion as it appears to be in 

 Man and the generality of Mammalia. In many Ruminants, and in 

 some of the Hog tribe, the muscular division of the canal opens into the 

 upper part of the third or vascular division, in such a manner that a 

 cul de sac occupies the commencement of the vascular bulb of the urethra, 

 as it is called by anatomists, into which the secretion of Cowper's glands 

 is poured without having been previously mixed with the seminal or 

 prostatic fluids. In some Rodents, as, for example, in the Squirrel and 

 the Marmot, the arrangement is still more curious ; for the cul de sac 

 of the bulb of the urethra in these creatures, which receives the secre- 

 tion of Cowper's glands, is lengthened out into a long tube that runs for 

 some distance beneath the proper urethra, and only joins that canal 

 near the extremity of the penis. 



(2473.) The body of the penis in the Mammalia, as in all other Verte- 

 brata possessed of such an organ, is composed of vascular erectile tissue ; 

 but now, besides the corpora cavernosa, which in Reptiles and Birds 

 formed the entire organ, another portion is superadded, destined to en- 

 close the canal of the urethra in a thick erectile sheath, and, moreover, to 

 form the glans, or most sensitive part of the intromittent apparatus. 



(2474.) The corpora cavernosa are now securely fixed to the bones of 

 the pelvis by two roots or crura ; and even in the Cetacea, where no 

 pelvis is met with, the ossa ischii exist, apparently, only for the purpose 

 of giving firm support to the origin of the parts in question. The size 

 of the corpora cavernosa in Man, and many other animals, is of itself 

 sufficient to give the needful rigidity to the parts during sexual excite- 

 ment ; but in some tribes an additional provision is required to ensure ade- 

 quate firmness. Thus in Monkeys, Bats, the Carnivora, the Rodentia, 

 and the Balcenidce among Cetaceans, a bone is imbedded in the substance 

 of the male organ, of which it forms a considerable part. Where this 

 bone exists, the corpora cavernosa are proportionately small, and the 

 fibrous walls of the penis are confounded with its periosteal covering. 



(2475.) The corpus spongiosum, likewise composed of erectile tissue, 

 is quite distinct from the cavernous bodies, and, as we have said before, 

 is only found in the Mammifera. It commences by a bulbous origin 

 that embraces the urethra, and it accompanies that canal quite to the 

 extremity of the penis, where it dilates into the glans. 



(2476.) The size and shape of the male organ varies, of course, in 

 every genus of quadrupeds, as does the form and texture of the glans. 

 To describe these would lead us into details of too little importance to be 

 noticed in a survey so general as that we are now taking ; nevertheless 

 we cannot entirely omit to notice the strange and unaccountable struc- 

 ture met with in some of the Rodent tribes, whereby the penis is ren- 



