644 ANATOMY OF VERTEBRATES. 



through the pelvis and terminates in the vestibular passage, anterior 

 to the orifice of the rectum, q. The vascular tissue of the penis 

 commences at the termination of the urogenital canal ; iJLis^sepa- 

 rated by a median septum into two lateral moieties, and both are 

 inclosed by a common dense fibrous sheath. The whole penis in 

 its collapsed and retracted state is about fifteen lines in length in 

 Echidna, and is concealed in a large preputial sheath. The ter- 

 minal half of the penis is formed by the glans, which, in Orni- 

 thorhynchus, presents a quadrilateral form, /, and is traversed by a 

 median longitudinal furrow upon both the upper and the under 

 surface. Its exterior is beset with numerous short and hard 

 epidermal spines : its extremity is bifurcate, and each lobe is 

 directed outward, and terminates in three or four spines, ib. k, /e, 

 much larger, but softer, than the rest, and which are usually re- 

 tracted in a depression. A longitudinal azygos ' levator ' muscle 

 runs along the upper surface of the penis ; it arises by two lateral 

 slips from the internal stratum, ib. n> of the protrusive sphincter, o. 

 Another longitudinal, but longer and more slender muscle, the 

 ' retractor penis,' ib. /;, arises from the base of the coccyx, and is 

 inserted into the origin of the penis near the termination of the 

 urogenital canal. The urethral canal of the penis begins by a 

 small orifice at its root, communicating with the termination of 

 the urogenital passage, and by the combined action of the last de- 

 scribed muscle with the ' sphincter cloacae ' it can be brought into 

 contact with the terminal papillae of the spermducts. Such tempo- 

 rary continuation of the urethral and seminal passages takes place 

 during the vigorous muscular and vascular actions of the parts in 

 coitu, the semen being then propelled from the one along the other 

 without escaping into the cloaca. Under ordinary circumstances, 

 as when the urine is transmitted along the urogenital passage, that 

 fluid escapes into the vestibule, and may there be blended, as in the 

 Bird, with the rectal excrement. The seminal urethra, commenc- 

 ing by the distinct aperture above described, is about a line in 

 diameter, and continues single to the middle of the glans, where it 

 divides into two canals ; each branch runs along the middle of the 

 bifurcation of the glans, and, when arrived at the base of the large 

 papillae, subdivides into smaller channels corresponding with the 

 number of the smaller ones, and opening upon their apices. If the 

 canal of the penis were slit open along its under part, and thus 

 converted into a groove, the male organs of the Ornithorhynchus 

 would be like those of a Tortoise ; and although the Mamma- 

 lian type of intromittent organ is manifested by the complete- 

 ness of the urethral canal, a resemblance to that of Lizards is 



