098 



1»R. E. Lo>>"BEHG OH THE 



[June 19, 



Ovibos must therefore be regarded as less distinct from the an- 

 cestral Cavicorn types from which the development of all three, 

 Ovibos, Oris, 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 4o mm. 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 the 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 

 abo\e description is taken, the length of the horn-core, lacking 

 vacuities, is 14 cm. The interior of this part of the horn-core is 



Fig. 6. 



Section of a part of the skull of the Musk-ox. 



In this figure the horn-core is sectioned longitudinally, and the 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 mm. 

 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 



