30 BINAR LONNBERG, ANATOMICAL NOTES ON EAST AFRICAN MAMMALS. 



In the year 1881 Forbes described^ the same organ of Dicerorhinus sumatrensis. 

 With regard to the peculiar » mushroom- or trumpet-shaped expansion » at the apex 

 of the penis this species agrees with Rh. unicornis. But the lateral lobes are very- 

 different in shape in the two animals. Forbes describes those of D. sumatrensis as 

 »two large oblong-oval lobes, of the same colour and substance as the rest of the 

 glans, which are free for the greater part of their length, and only attached to the 

 rest of the glans at their bases. The lobes he on the side of the dorsum of the 

 penis, and are closely approximated at their bases » — — — . 



The male organ of Diceros hicornis (conf. PI. II, Figs. 3 & 4) is of the same 

 general type as the same of the two other species mentioned above, and it is proved 

 by this that all three subgenera of Rhinoceros are rather alike in this respect, although 

 as a comparison shows there are specific differences to be found. 



The mushroom-, or trumpet-shaped organ at the apex has an oval disc with a 

 vertical diameter of about 20, and a horizontal of 13 V^ mm. in the present specimen. 

 The upper lobe is larger than the lower so that the distance from the lower edge to 

 the orifice of the urethra is only 7 mm. The peduncle of the disc is oval in section 

 with a vertical diameter of 13 and a horizontal of 9 mm. close behind the expansion, 

 but it increases gradually in thickness proximally. The terminal excavation or fossa 

 from the centre of which the just described mushroom -shaped appendix projects, is 

 deep and has high, rather thin-edged borders which form a kind of collar. Laterally 

 the height of this collar is about 17 mm. Ventrally it is somewhat broader still, 

 and curved down as a lip. All the way from the distal margin of this lip to its 

 base, and then up on the peduncle to the mushroom-like appendix runs in the median 

 line a small but distinct raphe. Dorsally in the median line the peduncle is con- 

 nected with the collar by means of a thick frenum which, however, unlike the ventral 

 raphe, does not extend on the peduncle itself beyond the direct connection. On the 

 dorsal surface of the penis above this frenum, thus on the dorsal surface of the collar, 

 there is a broad ridge which terminates just behind the edge of the collar with 

 a rounded knob which appears to have a thickened epiderm. Probably this knob 

 represents the end of corpus cavernosum penis. 



The two lateral lobes are very different in shape from those of the other two 

 species. They are nearly triangular in outline with straight vertical anterior contour, 

 somewhat curved upper contour and they sit on a long base (conf. PL II, Figs. 3 & 4). 

 Their anterior border is about 75 mm. behind the edge of the collar in the present 

 specimen. And the length of their base is about 58 mm. When the organ is at 

 rest the lobes are laid around the dorsal surface so that their borders meet mesially 

 and dorsally. They are a little thinner at their anterior border, but the average is 

 about 6 — 7 mm. in this stage. 



Basally on the ventral side of the penis-end between the same and the prepuce 

 there is a short but strong frenum and from this extends in the median line on the 

 ventral side a raphe which is continued to the lower lip of the collar and corresponds 



' Trans. Zool. Soc. London. Vol. XI. Part 4, p. 107. PI. XX. 



