MAMMALIA. 723 



or three distinct portions, each of which offers peculiarities worthy 

 of remark. The first part of the urethral tube is not unfrequently, 

 as in the human subject, more or less completely surrounded by 

 the prostate gland, and in such cases merits the name of " pro- 

 static portion;" but where, as in the Hedgehog, the prostates do 

 not enclose the commencement of the canal, this division of the 

 urethra does not exist. 



The second is the " muscular portion," extending from the 

 prostate to the root of the penis, and it is into this part that all 

 the generative secretions are poured from their respective ducts 

 (Jig. 33%, B, b, c, e, g, h). Externally, this division of the 

 urethra is enclosed by strong muscles (Jig. 332, A, i, i), which 

 by their convulsive contractions forcibly ejaculate the different 

 fluids concerned in impregnation, and thus secure an efficient in- 

 tromission of the seminal liquor into the female organs. 



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 com- 

 mencement 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 secretion 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. 



(855.) The body of the penis in the Mammalia, as in all other 

 Vertebrata 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 enclose the canal of the urethra in a thick 

 erectile sheath, and, moreover, to form the glans or most sensitive 

 part of the intromittent apparatus. 



The corpora cavernosa are now securely fixed to the bones of 

 the pelvis by two roots or crura ; and even in the CETACEA,where 



3 A 2 



