148 PROFESSOR OWEN ON THE GENUS DINORNIS. 
with comparisons of the homologous bones in the largest living wingless bird, Struthio 
camelus—to which end the admirable and usefully illustrated monograph by Professor 
Mivart, F.R.S., “On the Axial Skeleton of the Ostrich” ’, lends peculiar facilities. 
In these comparisons I adopt most of the technical terms of aspect and position 
proposed by Prof. Mivart, in addition to my own, and I subjoin, for the convenience of 
students, their vernacular equivalents :— 
preaxial = fore, anterior ; 
postaxial = back, hind, posterior ; 
dorsal or neural = upper; 
ventral or hemal = lower, under ; 
neurad = upward ; 
hemad = downward ; 
antero-posterior or prepostial = longitudinal, fore-and-aft ; 
dorso-ventral or neuro-hemal = vertical, high, deep ; 
lateral = side. 
medial = relating to the middle line or mid-vertical longitudinal plane of the body. 
ATLAS, or FIRST, VERTEBRA (natural size). 
Fig. 2. 

Aspects. 
Fig. 1, neural (or dorsal); 2, hemal (or ventral) ; 3, preaxial. 
The atlas vertebra of Dinornis robustus is described and figured in Zool. Trans. vol. v. 
p- 355, pl. 53. To the three figures there given, answering to the 2nd, 3rd, and 
4th in Mivart’s Memoir?, I here add views of the neural or dorsal, fig. 1, of the 
hemal or ventral, fig. 2, and of the ‘ preaxial,’ fig. 3, surfaces of the atlas of D. maat- 
mus, to complete the comparative illustrations of the bone in the genus Dinornis. 
The preaxial articular cup (fig. 38, ac) for the occipital condyle is formed in great 
part by the hypapophysis (simulating the centrum), the neural vacuity being supplied 
by the true centrum of the atlas (‘odontoid process,’ fig. 4, ca): the sides of this 
vacuity are formed by a pair of articular surfaces developed on the atlantal neur- 
* Trans. Zool. Soe, vol. viii. p. 385. > Tom. cit. p. 388, 
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