1908.] OKAPI AND GIRAFFE. 331 



dors. 1) of Giraffe are shown as are shown in the case of Okapi in 

 text-fig, 64. It is at once seen that there is no question of the 

 presence of a second pair of articular surfaces, of mediad position, 

 in Giraffe, so far as this articulation is concerned. 



Let us now go on to examine the posterior face of dors. 1, and 

 both faces of dors. 2 in Giraffe. These are drawn in text-fig. 67 

 for comparison with similar views of the same vertebrae of Okapi 

 drawn in text-fig. 66. 



The remarkable fact is at once obvious that the articulation 

 between doi'sal 1 and doi'sal 2 in Giraffe shows some of the 

 characters of the articulation between cervical 7 and dorsal 1 of 

 the Powell Cotton Okapi. There is on the posterior face of the 

 Giraffe's dors. 1, a lateral and a median articular surface which 

 are not separate from one another but confluent. And the same 

 is true as to the corresponding articular surface on the anterioi- 

 face of the Giraffe's dorsal 2. 



The lateral articular facet belonging to the true zygapophysis of 

 the cervical vertebrfe is in Giraffe continued into the dorsal 

 series — and does not disa^^pear until we come to the articulation 

 between dorsal 2 and dorsal 3 (see below as to Rhinocei'os). In 

 fact the first dorsal of the Giraffe is in this respect drawn (as it 

 were) into the cervical series. The bi-eak in the vertebral series 

 which occurs in Okaj)i (and normal Ungulata) between the anterior 

 and posterior faces of dorsal 1 is in Giraffe pushed down the 

 series and shows itself in the contrast between the anterior and 

 posterior faces of dorsal 2. There is, what has been called in 

 regard to such serial metameric elements of structure, " homoeosis " 

 of the first dorsal of the Giraffe — assimilating the articular facets 

 of that vertebra to those of the seventh cervical. 



The complete investigation of this question of the characters of 

 the last cervicals and first dorsals — and the transition from the 

 one group to the other and the greater or less abruptness of the 

 break Ijetween them in the whole Mammalian series, would form 

 an interesting enquiry. 



At present I must content myself with formulating the facts, 

 firstly, that in both Okapi and in Giraffe there is (as an exception 

 in Ungulata) a co-existence of lateral and mediad ax^ticular facets 

 of independent morphological value — at one of the vertebral 

 articulations at the base of the neck : and secondly, that the 

 articulation at which this occurs is in Okapi that between 

 cervical 7 and dorsal 1 — whereas in Giraffe it is shifted one pilace 

 backwards in the series and occurs between dorsal 1 and 

 dorsal 2. 



The relation of these 2:)eculiarities to the elongation of the 

 cervical region or to any other peculiarities of the animals in 

 question, is a matter for further enquiry. 



I am able to add to this the following additional observations 

 which I have made in the Museum of the Royal College of 



