OCR Text |
Show 698 DR. E. LONNBERG ON THE [Juue 19, Ovibos must therefore be regarded as less distinct from the ancestral Cavicorn types from which the development of all three, Ovibos, Ovis, and Bos, has diverged. The direction of the horn-cores of Ovibos is quite different at different ages, as has been described in the section treating of the development of the horns. The frontal sinuses (cf. fig. 5, p. 697) are very large anteriorly, so that in an old bull the vertical diameter of the lumen of these sinuses just above the anterior border of the brain-cavity, where at its deepest, measures 45 m m . Just in front of this place is a vertical and transverse septum situated above the lamina cribrosa. In front of this the frontal sinus forms one large cavity which is nearly undivided and measures 6 cm. in length. Posteriorly from the septum mentioned, the frontal sinus is divided into several loculi by vertical septa, as can be seen in the figure. The sinus extends into tbe base of the horn-core as far as 2-3 cm. reckoned from the lateral or inferior line of insertion of the horn-core (cf. fig. 6). But although the base of the horn-core is taken up by rather large vacuities, the greater part of the same is devoid of such (fig. 6). In the specimen (an old bull) from which the above description is taken, the length of the horn-core, lacking vacuities, is 14 cm. The interior of this part of the horn-core is Section of a part of the skull of tho Musk-ox. In this figure the born-core is sectioned longitudinally, and tbe anterior portion is moved to the side and exposes its interior surface on the right side of the figure. constituted by spongy bony tissue forming a layer about 20-24 mm. in thickness. This is again surrounded by a cortical layer, 6-10 m m. in thickness, of solid bone which, especially on the proximal side, is very dense (cf. fig. 6). The outer surface of the horn-core is,'as can be seen from the figures, very rugged and also partly spongy. From this description it may be concluded that the structure of the horn-cores of Ovibos is quite different from that of the Oxen, in |