MAY, 1921. AMERICAN MARSUPIAL, CENOLESTES OSGOOD. 63 



side. There are three pairs of Cowper's glands. The anterior pair are 

 elongate pear shape and open into the anterior part of the bulbous 

 urethra ventro-laterally. These have been designated in the figures as 

 Cowper's gland No. i. The two other pairs are situated dorso-laterally 

 just anterior to the base of the stalk of the corpus spongiosum and 

 have a common opening (PL IX, Fig. i). In fact the smaller one (No. 2) 

 appears to be scarcely more than a division of the larger (No. 3) since 

 they unite at an appreciable distance from the urethra. This gland 

 No. 3 is very large, several times larger than the others, even larger 

 than the paired testicles, and more than half the size of the enormous 

 prostate. It measures 12 mm. x 8 mm. Although not examined his- 

 tologically, its superficial appearance indicates a structure somewhat 

 different from that of gland No. i. Gland No. 2 appears to have the 

 same structure as No. 3, of which, as noted above, it is scarcely more than 

 a division. In Marmosa and Didelphis there are only two pairs of Cow- 

 per's glands, but in Peramys I find three as in Ccenolestes, the posterior 

 pairs being on a common stalk but showing no such discrepancy in size 

 as in Ccenolestes. The substance of gland No. i, except near the base, 

 appears as nearly solid, slightly granular tissue of a whitish color, whereas 

 No. 2 and No. 3 are highly fenestrated and spongy and even in gross 

 examination are seen to consist of numerous thin-walled tubules which 

 converge toward the duct and divide into branches toward the periphery 

 of the gland. In the glands of Marmosa and Didelphis, the same differ- 

 ence of structure obtains. In a pouch specimen of Macropus there are 

 three glands, as in C&nolestes, and the posterior ones have a common 

 stalk, but their structure seems identical with that of the anterior 

 pair. Histological study of fresh material is necessary before the 

 significance of the differences in these glands can be understood. 1 That 

 some of them may function as seminal vesicles is perhaps not im- 

 possible. 



The corpus cavernosum has its origin in a bulb invested with 

 muscles and situated slightly caudad of the first pair of Cowper's 

 glands. The stalk of this bulb, which is slightly bilobate, expands into 

 a layer around the ventral wall of the urethra and continues to the 

 base of the glans penis. The muscle covering the bulb of the corpus 

 cavernosum turns on itself and attaches on the stalk of the bulb instead 

 of continuing to form a levator penis as in the opossum. However, there 

 are three pairs of small thin muscles lying flat on the base of the corpus 

 cavernosum and the adjoining part of the bulbous urethra, some one of 

 which may be the homologue of the levator penis, although this seems 



1 Such work may have been done already, but the scope of the present study has 

 not extended to the literature in which it might be recorded. 



