374 DISCOVERY REPORTS 



length of the penis from the tip to the base of the bulbus. The bulbus forms two rounded 

 bosses at the base of the organ, the whole mass having a pear shape. It contains the 

 forks of the corpus cavernosum (the crus) but the main body of the bulbus consists of a 

 muscular mass — the ischio-cavernosus muscle or erector penis (Figs. 2/, 3/). 



The corpus cavernosum and corpus spongiosum. 



Before considering this muscle mass, however, it will be more convenient to describe 

 the corpus cavernosum itself. It forms the main erectile mechanism of the penis and 

 occupies the shaft of the organ from the terminal cone to the centre of the bulbus 

 (Figs. 2, 3 d, g). Distally, where there is a paucity of muscle fibres around the shaft, the 

 corpus occupies the greater part of the diameter of the penis and a transverse section in 

 the distal portion consists almost solely of the corpus cavernosum with its fibrous sheath 

 and accompanying corpus spongiosum (Fig. 4 C, D). Proximally and within the bulbus 

 the corpus is embedded in the muscle masses that surround that part of the organ. The 

 diameter of the portion of the corpus occupying the shaft of the penis decreases uni- 

 formly towards its distal extremity, but the shape of its cross-section varies considerably. 

 In a section across the terminal cone (Fig. 4 A, B, C) the corpus appears distinctly 

 bean-shaped, with an indentation posteriorly towards the corpus spongiosum. The 

 indentation forms a groove admitting the corpus spongiosum, running from near the tip 

 of the terminal cone to the base of the external part of the organ. At the root of the organ, 

 opposite the reflection of the panniculus carnosus on to its sheath, the section of the 

 corpus cavernosum (Fig. 4 D) becomes oval, the long axis of the oval being directed 

 antero-posteriorly. In the middle of the bulbus the corpus cavernosum forks to form 

 the crus (Figs. 2, 4). Within the shaft of the penis there is no sign whatever of any 

 division of the corpus cavernosum into two parts. The arms of the crus are directed 

 postero-laterally and make an angle of about 45 ° with one another. They are directed 

 into the posterior bosses of the bulbus where they terminate. Distally the arms of the 

 crus are nearly circular in cross-section (Fig. 4 G, H, I), proximally they take on an oval 

 outline. The extremities of the crura are attached to the pelvic bones by the interpelvic 

 ligament shortly to be mentioned. In the angle between the crura there is a small 

 medianly projecting lobe of cavernous tissue, forming a backwardly directed tongue 

 abutting upon the urethra at the commencement of the corpus spongiosum (Figs. 2, 

 4 G, H, a' 2 ). There is thus an undivided corpus cavernosum within the penis having the 

 form of a Y with a main stem occupying the shaft of the organ and the arms directed 

 backwards into the bulbus. The corpus has an outer investment of circular fibres and an 

 extensive inner core consisting of cavernous tissue of the usual structure with abundant 

 fibres and interstitial blood spaces. 



The following are the measurements in the 1-23 m. foetus: 



Length of the shaft of the corpus 3-5 cm. 



Length of each arm of the crus 3-0 



Diameter of the centre of the shaft 075 ,, 



Diameter of the centre of each ramus ... ... 0-5 ,, 



