10 RINAR LÖNNBERG, STUDIES ON RUMINANTS. 



deep downward curve indicating a slower growth of these parts. The curving of the 

 horn in a spiral is fa,cilit;tted by the fact that the originally lateral surface ^vhich con- 

 stitutes the inner side of the spiral is less convex than the median one which becomes 

 the peripherical side. 



During growth the horny sheath is moved iipwards or in a distal direction, bnt as 

 the development follo^vs the same main course all the time the sheath can slide evenly 

 över the core. The shape and strvicture of the sheath cannot be altered since it has once 

 been formed. The core must therefore follow closely the growth of the sheath and iill 

 up the space allotted to it. It is, so to say, monlded in the sheath. 



The thick horns of Oreas may be recognised as belonging to the same general type 

 as the two foregoing {Tragelaphus and Strepnceros). They are, however, considerably 

 modiiied. With regard to the outer appearance it is to be observed that the horns of 

 Oreas are shorter ^) and clunisier than those of Strepsiceros. They are also much less 

 twisted, with the main axis almost straight, and the rotation concerns only the proximal 

 part of the horn. This part is like the horns of Tragelapliun, spirally twisted roimd its 

 own axis. The core occupies less than two thirds of the horn which is a remarkable 

 difference from Tragelaphus. The distal third, or a little more, thus consists of solid 

 horn. Already this indicates an increase of the horny matter, but the thickness of the 

 sheath as well is enlarged. In the non twisted pai't the diameter of the horny wall is 

 from 7 mm. proximally, to 16 mm. at the tip of the core. In the twisted portion the 

 greatest diameter through the ridges is about 1 cm., and the shortest between them is 

 about V2 cm. As in the horn of Tragelaphus three ridges can be distinguished, but in 

 Oreeis the turns of the s])iral are less steep and form a greater angle with the longitudinal 

 axis of the horn. The relati^'e development of the three ridges is also different in both 

 genera compared. In Oreas the anterior ridge is the strongest, but the posterior ridge 

 on tlie median side is nearly as strong. The latero-posterior, on the contrary, (unlike the 

 condition found in Tragelaphus) is only little developed, its thickness being about 6 ram. 

 This gives of course anotlier shape to the horn. — The core of Oreas is still more aber- 

 rant from the type previously described. The proximal half of the core consists mainly 

 of a, coarse spongiosa surrounded by a compact exteriör wall. The latter does not, how- 

 ever show any great tliickness. At the base of the core it measures 3 — 5 mm. in sectioii. 

 The central spongiosa seems ba,sally to be rather loose and quite irregular in a region 

 corresponding to the one where the sinuses are found in Tragelaphus and Strepjsieeros. 

 A few centimetres from the base a, longitudinal arrangement of the elements can be seen 

 ^■ery plainly. On a, sagittal section the central spongiosa looks almost tubular. These 

 tubes in the tissue correspond to the canals for bloodvessels in the compact core of the 

 kudu, but the surrounding tissue itself has become spongious. The compact wall is here 

 from 4 to 7 mm. in thickness. The distal half of the core is almost entirely occupied 

 by a large caA^ity surrounded by a- comparatively thin case of bony tissue (conf. fig. 12, 

 Pl. II). This case consists chiefl}' of the outer compact la.yer alone, wliich measures 3 — 4 

 mm. in thickness. But on the imier surface of this wall some patches of an irregular 



..^) The leugth of the horns used for this iuvestigation was about 58 em. ■! /m .rii:;--: ■• 



