OCR Text |
Show 1900.] STRUCTURE OF THE MUSK-OX. 689 worn off in any higher degree than that a section from the tip of the horn in which such a horn-core fits fairly well corresponds to tbe original horn of that age, fig. 1 A is prepared. It is represented in the same plane as the main axis of the horn (as also is tbe case with figs. 1 B and C ) . Fig. 1 A should thus represent the horn of a young bull in the second autumn of its life. The longitudinal section of the horn of an adult bull, which is reproduced in fig. 2, shows that the horn has grown straight only until it reached a length of 5 cm. or hardly that, because already at that distance from the tip the originally ventral (later en distal) side of the horny sheath is thickened. Such a thickening of the ventral side of the horn produced by stronger growth of these parts effects, of course, the curving upwards of tbe tip of the horn. This curving upwards continues the whole of this period of growth, viz., the second summer of the animal's life. At the end of this summer the horns probably have attained a length of 35 cm., more or less, and their tips are at that time more raised above the facial line than at any later time. Fig. 2. Longitudinal section through a full-grown horn of the Musk-ox, showing lines indicating the growth at different periods. I have above used the words " period of growth," for I think that the horns are chiefly enlarged during that time of the year when the animals are able to procure food in sufficient quantities not only to sustain life, but also to add to their bulk. Theoretically such an assumption does not seem too hazardous considering the circumstances under which these animals live. But the probability of this is strengthened by the fact that on the longitudinal section of the horn are seen some lines of demarcation which are most easily interpreted as the limits between such parts as have been added during different periods of growth1. At " a " on fig. 2 1 Similar lines of demarcation are also seen on a longitudinal section of the horns of a common cow, and stand in that case plainly in connection with the rings at the base of the horn which in this country commonly are called " calf-rings," because it is known that a new ring, that is a new layer of horny |