126 
PROFESSORS T. W. BRIDGE AND A. C. HADDON 
As regards the modifications of the anterior vertebrae and their processes, Aucheno- 
glanis somewhat closely resembles Pseudohagrus or Rita. The first eight vertebrae 
are rigidly connected together, the ninth being the first of the flexibly articulated 
series. The body of the first vertebra is a thin slightly biconcave discoidal bone. 
The anterior face of the complex centrum (fig. 42, c.c.) is also discoidal with a 
relatively shallow concavity, but for the rest of its extent the centrum is laterally 
compressed, its posterior concavity being deep and almost tubular. The complex 
centrum is about half as long again as the centrum of the fifth vertebra. -The latter 
(u®) is similarly unsymmetrical in the relative depths of its concave surfaces, and 
nearly twice the length of any of the succeeding centra. Instead of the arch of the 
complex vertebra forming, as it almost invariably does, a continuous lamina of bone on 
each side of the neural canal, its anterior third is separated from the posterior two- 
thirds by a well-marked irregularly shaped cleft, which not only indicates the 
distinctness of the usually confluent arches of the third and fourth vertebrae, but also 
extends dorsal wards and is evident as a suture separating the lai’ge spinous process of 
the third from the rudimentary spine of the fourth vertebra. 
A continuous deposit of superficial bone thickens the lateral surfaces of the 
compressed centra of the complex and fifth vertebrae, and is also continued posteriorly 
in the form of stout ventro-lateral ridges as far as the seventh centrum. There is a 
deep median aortic groove on the ventral surfaces of these centra bounded by 
prominent lateral ridges. The posterior cardinal vein traverses, not a canal, but a 
deep groove (fig. 42, cd.g.) on the sides of the complex and fifth centra, between the 
dorsal edge of the superficial ossification and the roots of the adjacent transverse 
processes, and only for a short distance in the region of the dorsal lamina {d.l.) does 
the vein become completely surrounded by bone. The ventral margin of the anterior 
face of the complex centrum is produced downwards and laterally into a somewhat 
fan-shaped, transversely disposed, plate of bone (sv.jx) which is cleft in the median 
line for the passage of the dorsal aorta. Two similar but smaller processes (sv.p.^) are 
developed from the corresponding margin of the body of the first vertebra and become 
suturally applied to, without anchylosing with, the former pair. These paired bony 
outgrowths may, in part, represent the accessory articular processes of the complex 
and fifth vertebrae, but if this be so, there can be little doubt that they have been 
greatly strengthened by the extension of the superficial ossifications from the complex 
centrum into the mesial portion of the outer stratum of the tunica externa of the 
anterior wall of the air-bladder. 
The anterior division of the transverse process of the fourth vertebra {t.p.'^a.) is very 
stout, slightly decurved, and flattened antero-posteriorly towards its distal extremity, 
where it is applied to the expanded outer extremity of the inferior limb of the post- 
temporal. The posterior division is broad and flat continuous for the most 
part with the anterior division, but separated therefrom at its distal extremity by a 
wide cleft. The transverse process of the fifth vertebra is both longer and 
