392 
antero-posterior or prepostial = longitudinal, fore-and-att ; 
dorso-ventral or newro-hamal = vertical, high, deep ; 
lateral = side. . 
medial = velating 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, heemal (or ventral); 3, preaxial. 
The atlas vertebra of Dinornis robustus is described and figured (p. 169, Pl. LXII. 
figs. 4, 5, 6). 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. maai- 
mus, to complete the comparative illustrations of the bone in the genus Dinornis. 
The preaxial articular cup (fig. 5, ae) 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- 
apophyses, homotypal with the prezygapophyses in the succeeding vertebre. The 
vacuity is progressively encroached upon by the growth of the prezygapophyses, and, in 
the atlas of the aged individval of Dinornis maximus (fig. 3), it is reduced to the 
chink @ The neurapophyses have met and coalesced above the neural canal, which 
was not the case in the atlas of the younger, but full-grown, subject of D. robustus 
(loc. cit.). 
Assuming the atlas of Struthio camelus? to have been from a full-grown and mature 
individual, a similar confluence of the neurapophyses having taken place, the following 
differences are chiefly notable between it and the corresponding vertebra of Dinornis 
maximus. In the Ostrich the antarticular vacuity (not marked in Mivart’s figures), 
auswering to @ in fig. 8, remains much more widely open; the hypapophysial surface 
' Tom. cit. p. 388. * Tom. cit. p. 388, figs, 2-6. 
