376 DISCOVERY REPORTS 



The corpus cavernosum is a single structure in all Cetacea with the exception, 

 according to Anderson (1878, p. 474), of Platanista ga/igetica, where there are two 

 corpora cavernosa which separate to form a crus. Kiikenthal (1909, p. 575), however, 

 in describing the penis of Platanista, showed that the corpus cavernosum is unpaired in 

 the shaft, but forks distally into two lobes projecting upon the lateral aspects of the 

 penis. The corpus spongiosum is also a single structure within the shaft and accompanies 

 the forks of the divided cavernous body into the lateral lobes, but also sends a median 

 prolongation to the end of the penis, carrying the urethra and unaccompanied by the 

 corpus cavernosum. The corpus cavernosum of Platanista is thus only double distally 

 and is evidently secondarily derived from the single condition. It can be said, then, that 

 the Cetacea all show a single aseptate corpus. 



The corpus spongiosum urethrae, containing within it the urethral canal, occupies 

 a posterior position in the shaft of the penis (Figs. 2 e, 3 c, 4 b). It lies immediately 

 against the posterior aspect of the corpus cavernosum, and between the forks of the 

 crus it turns upwards and forwards through the centre of the "triangular ligament" 

 which lies between them, and terminates immediately below the root of the penis 

 where the urethra enters the prostatic part of its course. The corpus spongiosum has a 

 very small diameter compared with that of the corpus cavernosum and is invested by 

 the same fibrous sheath. The spongy tissue is denser and has fewer blood spaces than 

 that of the cavernous body. Peripherally, however, are a number of large blood sinuses 

 (Figs. 4 A, B b), passing in a longitudinal direction towards the terminal cone where 

 they increase greatly in number and extent and render that portion of the penis highly 

 vascular. 



At the middle of the terminal cone, immediately distal to the praeputium, the corpus 

 spongiosum is oval in section (Fig. 4 A, B) with the longer axis of the oval directed 

 transversely. In the shaft of the penis, however, the longer axis of the oval is at right 

 angles to its direction in the terminal cone and thus lies antero-posteriorly (Fig. 4 C). 

 In the shaft the corpus spongiosum fits exactly into a groove in the posterior face of the 

 cavernous body. It emerges from this groove on entering the muscular mass of the 

 bulbus and becomes circular in cross section (Fig. 4 E). Thereafter, until it turns 

 dorsally between the arms of the crus, the corpus spongiosum forms a projecting ridge 

 upon the posterior face of the corpus cavernosum. Throughout the length of the corpus 

 spongiosum its fibrous sheath is one with that of the corpus cavernosum and is directly 

 continuous with that of the prostata, where the urethra suddenly enlarges after leaving 

 the spongy part of its course. 



Between the arms of the crus there is a tract of fibres, formed by the junction of the 

 sheaths of the prostate, spongy body and the arms and shaft of the cavernous body. 

 This forms a part of the "triangular ligament" of Struthers (Fig. 2 h) which will be 

 mentioned shortly. 



There is no bulbus spongiosum and no penis bone, although a penis bone was 

 described by Turner in Balaena biscayensis (= B. glacialis). 



In Kogia breviceps only among the Cetacea is the corpus spongiosum known to fork 



