MALE GENITAL SYSTEM: INTERNAL ORGANS 379 



fibrous sheath of the cavernous crura (Fig. 2 h) and along its base with the fibres of the 

 " interpelvic ligament ". Upon the ventral and posterior face of the bulbus it is covered 

 by the bulbo-cavernosus muscle (Figs. 2 i, 3 i) which will be described presently. The 

 urethra and corpus spongiosum pass through the "triangular ligament" where they 

 turn dorsally between the crura from their passage through the shaft of the organ 

 (Figs. 2, 3). 



The ischio-cavernosus or erector penis muscle (Figs. 1 I 1 , 2/, 3/, 4^) appears to be 

 powerfully developed in all Cetacea. According to Meek (1918) it has, in the porpoise, 

 an attachment extending along the whole length of the pelvic bone, which it envelops 

 completely. In Mesoplodon (Anthony, 1922, p. 97) it has a double origin, one from the 

 whole length of the pelvic bone and the other from a small circular aponeurotic centre 

 behind the pelvic bone. In Kogia (Benham, 1901), where no pelvic bone exists, there is 

 a small ligamentous patch at the posterior end of the muscle from which the fibres 

 radiate, and this small ligamentous patch is itself attached to the sphincter ani by a small 

 separate muscle. In all Cetacea the main body of the muscle forms a large muscle mass 

 confined to the cavernous body and forming the pear-shaped bulbus. 



In Balaena (Struthers, 1881) the ischio-cavernosus takes origin from the inner border 

 only of the pelvic bone and does not envelop it, by far the greater part of the muscle 

 being confined to the bulbus. In Balaenoptera physalus the ischial part of this muscle is 

 small and unimportant. Daudt (1898, p. 288) says: " Der Musculus Ischio-cavernosus, 

 welcher vom hinteren Ende des Beckenknochens kommt, der bei seinem Beginn nur 

 von wenigen sehnigen Faserziigen durchsetzt ist und noch nicht mit dem von Struthers 

 beschreibenen Ligamentum Interpelvicum beginnt, umhullt anfangs die beiden Corpora 

 Cavernosa seitlich und teils dorsal und teils ventral ". In the specimens examined in the 

 present work the ischiac attachments of the ischio-cavernosus muscle appeared to be 

 fibrous but slight, and the fibrous part joined other fibres coming from the transverse 

 tract at the base of the bulbus (Fig. 27), the "interpelvic ligament". 



The main fibres of the ischio-cavernosus muscle take origin from the lateral and 

 posterior surfaces of the cavernous crura. After a short course forwards the fibres turn 

 towards the anterior face of the penis and meet those of the opposite side in a median 

 raphe. The muscle mass thins out very greatly upon the shaft of the organ, where its 

 fibres have a more longitudinal direction. Anteriorly, at the extreme base of the bulbus, 

 is an area between the ischio-cavernosus muscles of the two sides where the " transverse 

 ligament" rests between the arms of the crus upon the ventral face of the prostate. 



Struthers described and figured a semicircular septum dividing the ischio-cavernosus 

 muscle into a proximal or posterior moiety, confined to the bulbus penis, and a distal or 

 anterior moiety confined to the shaft of the penis. This, however, has not been con- 

 firmed in the present work. The muscle formed a single continuous mass adherent to 

 the penis, and other authors, notably Daudt, who have examined the genital muscles, do 

 not mention this semicircular septum of Struthers. 



From the slight extent of that part of the ischio-cavernosus muscle attached to the 

 pelvic bone it would seem that the function of this muscle must be to erect the penis, 



