VOL. XXIV.] PHILOSOPHICAL TRANSACTIONS. A/ 



conceive. Nature would never have been so careful in this animal, in making 

 a double glans, and contriving two distinct apertures in the glans, when its 

 penis is erected, if the propagation of the species had not depended on it: 

 doubtless it was for that end chiefly, that the penis of this animal differs so 

 much from what we meet with in others. Nor could its penis in these circum- 

 stances be exposed in a praepuce, as in other quadrupeds, by reason of the 

 numerous accidents that would certainly occur in this animal's way of living* 

 nor could its penis have been thus retracted when not erected and sufficiently ex- 

 truded, when it is, if (as in other animals that are also retromingent) the penis 

 here had been fastened to the ossa pubis. 



Thus we see nature in these instances, as frequently occurs in many others, 

 accomplishes the same ends by different methods. Although there are no 

 vesiculae seminales in this animal as in dogs, weasels, &c. yet we find its penis 

 without a bone in it, as in those; but then we meet here with additional 

 contrivances to maintain its erection: not only the sphincter muscle of the 

 cloaca, fig. 3, of the male opossum, but that of the female also closely embraces 

 its penis in coition, and effectually retard the refluent blood from its corpora 

 cavernosa, by compressing the veins of the penis e, fig. 4. Nor could the 

 penis of this animal be framed like that in boars, rams, bulls, &c. in whom the 

 corpora cavernosa are too large, when not erected, to be secured within the 

 cloaca of this animal. 



The Explanation of the Figures. — Fig. 1, pi. 5, shows the external appear- 

 ance of the genitals of the male opossum, abcc the anus or cloaca; Aits 

 lower part, which leads to the rectum; b its upper part, or the orifice of the 

 praeputium, whence the urine and the penis is extruded; cc two small apertures, 

 whence the yellowish coloured liquor, that had the peculiar foetor of the animal, 

 had its exit; d the scrotum, just large enough to contain the testes; e that 

 part of the abdomen, where the marsupium is seen in the female, which here 

 appears a little more depressed than in other animals, but cannot retain the 

 young ones, as the pouch of the female does; pp the two thumbs of the hind 

 feet or hands. 



Fig. 2 represents the foreparts of the organs of generation dissected from the 

 male opossum; aa the body of the penis; ab the forked glans; cc the muscles 

 analogous to the directores penis in men and other animals, which here inclose 

 the bulbi of the cavernous bodies of the penis; dd the two corpora cavernosa 

 penis, before they join and make the body of the penis; ee parts of the two 

 bulbs of the cavernous body of the urethra; Gff a pair of muscles, whose two 

 tendons ff pass through two ligaments or pulleys on the ossa ^ubis, and are 

 afterwards united into one tendon g, inserted into the dorsum penis, and serve 



