378 DISCOVERY REPORTS 



concavity which they compared with a glans. From its opening the urethra passes 

 obliquely through the tip of the cone to its posterior position in the penis. In transverse 

 section the part of the canal traversing the cone has a T-shape (Fig. 4 A, B), the cross 

 arm of the T lying against the corpus cavernosum. Where the corpus spongiosum 

 occupies a groove in the posterior face of the corpus cavernosum within the shaft of the 

 penis, the urethral canal is an antero-posteriorly directed slit in transverse section 

 (Fig. 4 C) and lies centrally within the spongy body. At the base of the shaft the section 

 of the urethra again becomes T-shaped (Fig. 4 D). Within the bulbus it is circular 

 (Fig. 4 E), and finally, upon turning dorsally and just before widening to the prostate 

 part of its course, it becomes a transversely directed slit (Fig. 4 F, G, H). 



The musculature of the penis 



We may now describe the musculature of the penis with reference to the cavernous 

 and spongy structures. 



The retraction of the penis, causing its withdrawal into the penis sac, is brought 

 about by a pair of strap-like muscles (Figs. 2 b, 36, 4/) lying along the whole of the 

 posterior face of the organ. These — the retractores penis — take origin from the walls of 

 the rectum immediately posterior and dorsal to the bulbus, and after running apposed 

 to one another along the posterior face of the organ, flatten out distally and are inserted 

 into the praeputial fold (Figs. 2, 3). Each muscle appears to have a double insertion 

 upon the praeputium. Close to its insertion each retractor forks, so that one arm of the 

 fork on each side is inserted into the praeputial fold laterally and the other posteriorly 

 close to its antimere. The retraction of the penis is brought about solely by the action of 

 these muscles, so that in its retracted state the length of the penis is only apparently, but 

 not actually diminished, becoming bent within the body cavity into a sigmoid curve as 

 figured by Daudt (1898, pi. 9, fig. 16) for Phocaena and by Kiikenthal (1909, Taf. 49, 

 fig. 25) for the same species. 



The ischio-cavernosus or erector penis muscle (Figs. 1 F, 2/, 3/, 4^), together with 

 all the muscles of the genital and pelvic region in the male Fin whale, were studied in 

 detail by Struthers (1893), whose figures have formed the bases of all subsequent 

 accounts. 



Between the ischial portions of the two pelvic bones a ligament extends which 

 Struthers called the ligamentum interpelvicum. In its course between the two pelvic 

 bones it involves the posterior extremities of the arms of the crus (Figs. 27, 37). 

 Meek (191 8) mentions also a strong ligament in the porpoise extending to a point on 

 the pelvic bones near their ischial extremities and carrying the two arms of the crura. 

 In Balaena, according to Struthers (1881), this ligament is powerful; but in the Fin 

 whale it is feebly developed, as stated by Daudt (1898, p. 288), and is not the broad tract 

 of fibres described and figured by Struthers (1893) for this whale. The triangular space 

 between the arms of the crura is further filled by a ligament (Figs. 2 h, 3 h) with fibres 

 directed transversely between the arms. This is the " triangular ligament" of Struthers. 

 The triangular fibrous tract is continuous at its apex and along two sides with the 



