1902.] OF HORNS AND ANTLERS. 213 



Below and between them are numerous hairs, some of which reach 

 the surface and are imbedded in the horny mass, others are 

 hemmed in and suppressed. 



The rest is best explained by a diagram. The important point 

 is that the cartilage, dense and hyaline, and in active proliferation 

 near the periost, changes further inwards into clusters of cells 

 which show the same features and the same thyanine- staining 

 action as the so-called muco-cartilage. Towards the strands of 

 young connective-tissue, which becomes more prominent as we 

 proceed inwards, the muco-cartilage cells show a breaking vip of 

 their nuclei, so that only a glassy mass remains, interspersed with 

 debris of the cells and their nuclei. [When not dccalcij&ed, this 

 mass is somewhat opaque and bluish owing to infiltration with 

 calcareous salts. All this hyaline ground- substance is destroyed 

 by giant cells which are active on the margin and a little further 

 down. The place of the vanishing cartilage is taken up by the 

 network of connective-tissvie strands, and in this appear very 

 active marrow-cells, and osteoblasts which build up trabeculse of 

 bone. Consequently the cartilage is not wanted at all for the 

 construction of the cone. This is also obvious from the fact, 

 mentioned above, that a few months after birth the cone continues 

 to grow long after the last trace of cartilage has vanished. The 

 cartilage is in fact an invader of dormant scleroblast- cells in the 

 periost, different from osteoblasts.] Concerning the horny sheath, 

 I have to mention two important points which have hitherto 

 escaped notice. First, the inclusion and gradual suppression of 

 hairs by the proliferating intercrinal horn-substance. Even in 

 old specimens of cattle-horns hairs become imbedded in the horn- 

 sheath, which in opposition to the bone-core always exhibits basal 

 growth. Secondly, the fact that calves, when several months old, 

 shed the first juvenile hornshoe. This is not always cast ofi" in 

 one piece ; it may be frayed off, but this is a process very different 

 from the incessant wear and tear of the permanent horn-sheath 

 of the adult. The shed portion so to speak, the first generation 

 of the horn, is more porous, less solid than the permanent horn, 

 from the base of which it becomes separated to the extent of 

 several centimetres, as shown in the illustration (text-fig. 25, 

 p. 216). The whole process recalls the relation of the neossoptile 

 to the teleoptile or permanent feather, and still more the shedding 

 of our own foetal finger-nails. 



III. Antilocapra. 



Not much more is known about the development of the Prong- 

 buck's horns than what Forbes and, recently, N"itsche have 

 described. Nitsche has shown that the sheath is an aggregation 

 of sparse hairs connected by much " intercrinal " horn-substance, 

 the whole process resembling somewhat the pathological ichthyosis 

 of calves. He has also shown that the prong is formed entirely 

 by the horn- sheath, and that there is no corresponding outgrowth 



