692 DB. E. LONNBEEG ON THE [June 19, 



of which the exostoses consist is reabsorbed and replaced by horny 

 layers. It may be said metaphorically that the horny sheath eats 

 down into the bony mass, which thus gets a rugged and pitted sur- 

 face such as is seen on figs. 3 and 1 C. The pits and holes are filled 

 up with horny substance. The interior surface of the basal part 

 of the horny sheath is, in correspondence with this, densely beset 

 with strong warty prominences, as can be seen in fig. 4. By this 

 arrangement the horns become exceedingly strongly fixed to the 

 skull, which is needed on account of the downward direction of the 

 horn-core, which does not at all extend into the upward curve of 

 the horn itself ; every weight on or resistance against the hooked 

 tip of the horn tends to pull the horny sheath of the core, and this 

 would rather easily take place if it was not for this clinching of the 



Fig. 4. 



Lateral yiew of a longitudinal section of a horn of an old male Musk-ox, 

 showing the structure of the inner part of the basal horn-layer, which has 

 taken the place of the exostoses, and the lines indicating the periodical 

 growth of the same. 



basal parts to the bony mass of the skull. The horn cannot 

 consequently be regarded as ready for use as a weapon before it is 

 fixed to the skull in the manner described. Such an arrangement 

 is also much more suitable than if the core should extend into the 

 upward curve of the horn, because, as it is, the horn at the bend 

 can be entirely tilled up with homy substance, and thus be made 

 much stronger at this place, on which the heaviness of a charge on 

 the tip of the horn works most. If the core extended through the 

 curve for the purpose of fixing the sheath, the horn at this place 

 should consist of a comparatively thin layer of horny substance 

 which could be relatively easily bent, and a central bone which 

 would be broken even by a moderate charge. 



That it is of great importance that the horn should be strong at 

 the curve, and that it is used for heavy work, is proved by the fact 

 that one of the bulls shot by Professor Nathorst had the tip of one 

 of its horns broken in the bend at a place where it was 4| cm. 

 thick. Such a breaking needs certainly a formidable strength and 

 a heavy load. 



The reabsorbing of the great exostoses and their replacement by 



