330 SIR RAY LAXKESTER ON THE [^P^'- ^? 



as shown in text-fig. 66, that it is obvious that the niediad articular 

 surfaces Avhich co-exist in cerv. 7 (posterior face) and dors. 1 

 (anterior face) with the lateral articular surfaces, are new and 

 independent morphological entities and are identical with the 

 articular surfaces of the dorsal vertebrae, whilst the laterally- 

 placed articular surfaces of the cervicals raised upon distinct 

 " zygapophyses " have no existence in the dorsal series except on 

 the anterior face of the first dorsal. 



It seems to me that we are entitled to conclude from the 

 specimen here figured (text-figs. 64 and 66) that the zygapophyses of 

 the cervical vertebrae of the Mammalian series are not merely^ in 

 a diff'erent position from that occupied by the articular facets of 

 the dorsal vertebrae, but that the cervical and the dorsal articular 

 ■surfaces are distinct morphological entities. The articular facet is 

 not bodily " shifted " in position, v>"hen we pass from cervical to 

 dorsal, but a distinct and independent mediad facet is substituted 

 for the lateral facet. At the same time it must be recognised 

 that the two articular facets can become confluent, and that one 

 is to be regarded as an extension and " pullulation" of the other. 

 So far as I am aware, this is a new observation. 



I hasten to say that in the cerv. 7 and dors. 1 of another 

 skeleton of Okapi (the property of Mr. Walter Rothschild) the 

 two articular facets of each side drawn in text-fig. 64 are not 

 marked off from each other, but confluent and ill-defined. The 

 vertebrae of that skeleton difFei' in many remarkable points of 

 size and proportions from those of the Powell Cotton skeleton. 

 Though the Rothschild skeleton is that of a ver}^ young animal 

 far from complete in growth, whilst the Powell Cotton skeleton 

 is that of a full-grown animal with nearly adult dentition, yet 

 many parts of the vertebrae of the younger animal are much 

 larger than the same parts in the older animal. At the same 

 time in other details the latter shows the greater size. It 

 is possible that the Powell Cotton specimen is exceptional and 

 abnormal, or that it belongs to a local race difiering from that to 

 which the Rothschild skeleton belongs. Or again, and this I think 

 to be the most likely case, it seems from the variability of Okapi 

 in regard to the striping of the skin and various proportions of 

 the skull, also as to the symmetry of the horns of either side 

 and as to the molar teeth, that there is great range of variation in 

 the species — and that this vaiiability extends even to such points 

 as the exact form of the vertebrae and the development of articular 

 facets connecting successive vertebrae. It is also possible that the 

 absence of a distinct second pair of facets at the articulation 

 between cerv. 7 and doi's. 1 in this particular specimen of Okapi 

 is due to its immature stage of growth. 



A comparison of these vertebrae of Okapi with those of Giraife — 

 in regard to the zygapophyses and articular surfaces or facets — 

 hecomes now especially interesting. 



In text-fig. 65 the same views of the two vertebrae (cerv. 7 and 



