392 



MONOTREMATA. 



Fig. 190. 





Male organs, Ornithorhynchus. (Meckel.) 



The Monotremes are true testlconda, and in 

 this respect differ from the Marsupial animals. 

 In the Echidna each testicle is situated imme- 

 diately below, or sacrad of, the kidney, and is 

 suspended to that gland by a fold of peritoneum; 

 the same fold is continued to the neck of the 

 bladder, inclosing the vas deferens, which is 

 disposed in a series of close transverse folds 

 throughout its whole course. It corresponds 

 closely, in these respects, with the Ornitho- 

 rhynchus. In neither Monotreme is there any 

 disparity of size between the right and left 

 testicle : the latter is figured in situ at u',Jig.\Q7. 

 The vas defer ens (fig. 190, f) emerges from the 

 upper or atlantal extremity of the testis (e) ; 

 and, from its peculiarly extended, plicated, or 

 folded course, seems to prolong the epididymis 

 nearly to the neck of the bladder ; the folds 

 gradually diminish, and the duct itself enlarges, 

 as it approaches its termination, which is in the 

 beginning of the urogenital canal (g). This 

 canal is continued through the pelvis and termi- 

 nates in the vestibular passage, anterior to the 

 orifice of the rectum (q). 



The vascular tissue of the penis com- 

 mences at the termination of the urogenital 

 canal; it is separated by a median septum 

 into two lateral moieties, and both are in- 

 closed by a common dense fibrous sheath. 

 The whole penis in its collapsed and retracted 

 state is about fifteen lines in length, and is con- 

 cealed in a large preputial sheath. The ter- 

 minal half of the penis is formed by the glans, 

 which presents a quadrilateral form, and is 

 traversed by a median longitudinal furrow upon 

 both the upper and the under surface. Its ex- 

 terior is beset with numerous short and hard 

 epidermal spines : its extremity is bifurcated, 

 and each lobe is directed outwards and termi- 



nates in three or four spines, (/c, /c,) much 

 larger, but softer, than the rest, and which are 

 usually retracted 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 

 (w) of the protrusive sphincter. Another lon- 

 gitudinal but longer and more slender muscle, 

 the retractor penis, (fig- 190, p,) arises from 

 the upper part of the base of the tail, bends 

 downwards over the caudal muscles and vessels, 

 and is inserted into the origin of the penis near 

 the termination of the urogenital canal. The 

 true urethra or canal of the penis begins by a 

 small orifice at the root of the penis, near the 

 termination of the urogenital passage, and by 

 the combined action of the last described 

 muscle with the sphincter cloacae, it can be 

 brought into closer approximation with the uro- 

 genital passage. It must be supposed that 

 this temporary continuation of the urethra and 

 urogenital passages takes place during the vigo- 

 rous muscular and vascular actions of the parts 

 in coitu, and that the semen is then propelled 

 from the one along the other without escaping 

 into the common vestibular compartment of the 

 cloaca. Under ordinary circumstances, as 

 when the urine is transmitted along the uro- 

 genital passage, it must escape into the vesti- 

 bule, and may there be blended, as in the Bird, 

 with the rectal excrement. The true seminal 

 urethra, commencing by the distinct aperture, 

 as 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 cor- 

 responding with the number of the papilla?, 

 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 then 

 essentially like those of a Tortoise. The adhe- 

 sion to the Mammalian type is manifested in a 

 highly interesting manner by the completeness 

 of the urethral canal, whilst the affinity to the 

 Marsupial order is evinced in its bifurcation, 

 corresponding with that of the glans itself. Had 

 the penis been neither perforated nor grooved, 

 as Cuvier once believed, the structure would 

 have been extremely anomalous. That the 

 existence of a penis is essentially and subordi- 

 nately related to the sexual organs and not to the 

 renal, is beautifully illustrated by the complete 

 separation of the uro-urethral from the semino- 

 urethral passages in the Monotremata. 



The modifications by which the male organs 

 in the Echidna differ from those of the Ornithor- 

 hynchus, are confined to the glans penis, which 

 divides into four mammiloid processes, rough- 

 ened by minute papillae, and terminated by a 

 depression in which is the branch of the semi- 

 nal canal that traverses each process. Cowper's 

 glands C/g.180, k, k, andjig.190, K) are of large 

 relative size; they are situated between the base 

 of the penis, the arch of the ischium, and internal 

 part of the thigh : their secretion is carried 

 by a long and slender duct (Jig. 190, i)into the 



