OCR Text |
Show 196 ON HORN-GROWTH IN A CASTRATED PRONGBUCK. [Mai'. 21, sheaths united by a solid central core. The proximal, or fifth, is separated from the fourth by a deep cleft extending more than half way round the sheath. It measures 1 inches, and presents on its concave (morphologically anterior) side a small but distinct and sharp tubercle representing the prong. The fourth, measuring 1 1 inches, is itself subdivided into two by a deep cleft, suggesting that it may represent two short, partially-separated sheaths. The third, which is marked off externally from the fourth by a deep but narrow cleft, measures 1^ inches. Neither the fourth nor the third shows a trace of the prong. The second, measuring lg inches, has, however, a very pronounced tubercle; it is separated from the third by a deep cleft completely encircling the sheath. A similar complete cleft also marks the divisional line between the second and first, which is curved as in the right horn-sheath and measures about 2 inches. In longitudinal section this sheath is also like that of the right side. The individual components are firmly welded together by the solid central core, and the cortical layer is subdivided by oblique clefts, some of which fall short of the periphery of the sheath and are visible only in section, while others are carried through to the surface and mark the spaces between the sheaths. The lengths of the latter from base to apex, as shown in section, are as follows:-Nos. 5-2 about 21 inches, no. 1 about 2^ inches. The left horn I removed from the animal's head myself. It was loose, and the fibres at its base were easily ruptured by rotation. The sheath came partially away from the horn-core, leaving it covered with a horny cap, the last-formed sheath. This cap, however, was firmly united apic-ally to the angle of the socket of the antecedent sheath by a solid horny strand continuous with the central core traversing the length of the composite horn-sheath and binding its constituents together. This strand (text-fig. 29, A) had to be severed with a knife before the sheath could be removed. The presence of this horny cap upon the left horn-core and the naked and bleeding condition of the right one sufficiently explain the presence of six horn-sheaths in the right and five in the left detached composite sheath. The effects of castration on the horns of the Prongbuck may thus be summarised as follows :- 1. Modification of the Horn-cores.- These are shortened and bent obliquely forwards and outwards at the apex, causing the sheath to project in the direction of the nose. 2. Modifications of the Horn-sheath :- a. Shedding of the sheath does not take place. b. The first-formed sheath is normal in shape, and at the time for shedding breaks away from the second except at the point where the apex of the latter joins the angle of the cup of the former. A similar partial severance separates the succeeding sheaths from each other. |