1907,] HORNS OF THE GIRAFFE. 109 



pei'iosteum ; and (3) that in a much younger di^iecl skull there is 

 no indication on the cranial wall of any " outgroAvth." 



We shall not be in a position to S|)eak deiinitely until other 

 fcetal Gii-affes of younger stages have been examined by proper 

 histological methods ; but it seems legitimate to consider the 

 lateral ossicones of the Giraffe, and therefore of the Okapi, as 

 originating in a fibrous osteogenetic mass which gives rise to a 

 protrusion of the integument and originates in the connective 

 tissue of the integument rather than in the osteogenetic tissue of 

 the cranial roof, from which it is separated by a dense membranovis 

 periosteum. 



The lateral ossicones of the Girajff-e appear to have the same 

 nature and "mode of origin as has the centrally -placed ossicone of 

 the same animal. This median ossicone is variable in size, and 

 does not appear until many years after birth when growth is 

 nearly complete. The histological processes by which the median 

 ossicone is formed have never yet been studied, but it is practically 

 certain that it forms not as an outgrowth of the bone of the 

 cranial roof, but as a " dermal " or tegumentary growth external 

 to and independent of the cranial bone. 



The same pi-ocess which leads in the Giraffe to the formation of 

 a median ossicone, in some cases becomes specially active and leads 

 to the formation of additional "■ supernumerary " sub-tegumental 

 ossifications. Thus two such of smaller size than the normal 

 median ossicone are seen in the median line in a skull of Girafie 

 in the British Museum, in which bony deposits on the margin 

 of the orbit are also seen. The skuU of Okapi brought by 

 Capt. Boyd Alexander from the Welle Eiver shows such an 

 exceptional sub-tegumental bony deposit on the margin of each 

 orbit ; and it is to be noticed that both in Giraffes and Okapis in 

 old individuals the base of each ossicone spreads very widely as a 

 thin encrusting layer, so as to involve much of the frontal in 

 specimens of Giraffe and a large surface of the parietal in the case 

 of Okapi. 



These superficial ossicones and their outspreading marginal 

 growths of the Giraffidfe cannot be accurately marked off in later 

 life, although they can be sepai-ated in earlier life, from the highly 

 important upgrowths or " tumescences " (as I previously called 

 them) of the cranial bones over which they lie. The completed 

 lateral horn of the Girafie consists very largely of a conical up- 

 growth of the parietal bone, and also of the frontal bone — occupied 

 by an air-sinus — developed between the tabulfe of the bone. The 

 basal region of the upgrowth involves the frontal bone more 

 largely than the parietal. The originally independent ossicone 

 contributes but a small amount to the whole bulk of the structure. 

 It forms mei-ely the terminal knob, and is fitted over the tumes- 

 cence like a superficial investment which dwindles in thickness as 

 it descends the cone until it becomes a mere film. 



The position of the lateral and median ossicones in an adult 



