3 8o 



DISCOVERY REPORTS 



not by pulling upon the pelvic bone, but by compressing the proximal end of the 

 corpus cavernosum and so driving the blood forward towards the terminal cone. The 

 muscle will also have the effect to a less extent of squeezing the corpus spongiosum and 

 urethra, driving the seminal fluid forwards during the orgasm. Yves Delage (1885, 

 p. 131), however, was of opinion that the envelope of the corpus cavernosum was too 

 thick to allow compression by the ischio-cavernosus muscle. He believed that the 

 ischio-cavernosus acted by dragging the penis backwards, or, through the independent 

 action of the muscles of one side, by pulling the penis to one side or the other during the 

 act of copulation. However, the ischiac attachment is almost certainly too small for such 

 an action as this. The immense mass of muscle confined almost entirely to the face of 

 the corpus cavernosum can only have a compressor action. 



The bulbo-cavernosus muscle lies between the arms of the cavernous crura (Figs. 

 1 / 10 , 2 i, 3 i) immediately ventral and posterior to the "transverse ligament", with the 

 fibres of which the deeper fasciculi of the muscle intermingle. The bulbo-cavernosus is 

 overlaid in ventral view by the two retractores penis and posteriorly abuts upon the 

 levator ani. The fasciculi arise from the inner ventral surfaces of the posterior portions 

 of the arms of the crura and are inserted, after a short inward and backward course, 

 upon a median fibrous raphe. The muscle must act by approximating the two arms of 

 the crura, thus assisting in the erection of the penis. 



^ft^^. 



The prostata 



The part of the urethra extending from the termination of the corpus spongiosum at 

 the base of the bulbus penis forward to the verumontanum, where the vasa deferentia 

 join the urinary canal, has been named the prostate 

 portion of the urethra (Fig. 3/). In the foetus, 1-23111. 

 in length, this part of the urino-genital canal measured 

 2-0 cm. and had a cross-section of 1-3 cm. That is to 

 say the prostata was somewhat less than a quarter as 

 long as the part of the urethra within the corpus 

 spongiosum. The prostate part of the urethra has an 

 antero-posterior course and inclines slightly ventral- 

 wards towards its anterior extremity. The urethral 

 canal widens very considerably in the prostatic part 

 of its course; but a ridge, rising up from the dorsal Fig. 5. Transverse section across the 

 wall of the canal and increasing in height from be- prostata of a 1-23 m. Fin whale foetus 

 hind forwards (Figs. 3, 5, 6), converts the cross- at the seminal pores, (x 4.) 

 section of the lumen into a crescent with dorsally 

 directed horns (Fig. 5). Very numerous racemose 

 glands open into the grooves formed by the horns of 



this crescent and less abundantly upon the surface of e - Unstriped muscles of the glands. 

 the ridge itself. The ridge is reinforced by a septum of longitudinal smooth muscles 

 (Fig. 5) which are pronounced and strongly developed anteriorly but less so posteriorly. 





a. Seminal pores. 



b. Urino-genital canal. 



c. Glandulae urethrales. 



d. Compressor prostatae muscle. 



