196 
PROFESSORS T. W. BRIDGE AND A. C. HADDON 
together, their union being* due to the close sutural articulation of their respective 
neural arches, and to the continuous investment of their centra by superficial 
ossifications. The sixth vertebra (v.®) is quite free. The spinous processes of the 
third and fourth vertebrae are distinct except at their* roots, and incline forwards and 
backwards respectively. The rigid connection of the skull with the vertebral 
column is secured by the intimate articulation of the arch and spine of the third 
vertebra with the exoccipitals and supraoccipital. 
The transverse process of the fourth vertebra has a broad, flat root but distally is 
cleft into short anterior and posterior divisions of which the former is 
bent downwards and flattened antero-posteriorly, while the latter is somewhat 
expanded in a horizontal plane and angulated at its free distal extremity. The 
transverse process of the fifth vertebra is very similar to the posterior division 
of the preceding process, and at its root is partially confluent therewith. The 
succeeding transverse process carries the first rib and is quite distinct from 
the foregoing. 
Superficial ossifications invest and considerably thicken the lateral surfaces of the 
complex and fifth vertebral centra, and by their produced ventral margins form the 
lateral walls of a median aortic groove. Anteriorly, the ossifications appear to 
terminate on the ventral surface of the complex centrum, near its junction with the 
body of the first vertebra, in a vertically disposed fan-shaped ridge, which is cleft in 
the centre for the transmission of the dorsal aorta (fig. 82, sv.p.). Dorsally, the 
ossifications terminate in a free edge near the roots of the contiguous transverse 
processes, which forms the inferior lip of a groove for the posterior cardinal vein 
and the anterior lobe of the mesonephros. On each of the lateral surfaces of the 
complex centrum, close to the root of the fan-shaped subvertebral process, there is a 
somewhat elongated radial nodule (r.??.), which is but loosely connected with the centrum 
by fibrous tissue, and also in the same way with a slender spicule of bone (dorsal 
lamina) that extends outwards beneath the posterior cardinal vein and finally blends 
with a longitudinal ridge on the ventral surface of the root of the transverse process of 
the fourth vertebra wdiich forms the dorsal or outer margin of the cardinal groove. 
The post-temporal {pt.s.,pt.i.) is normal and has the usual relations to the distal 
extremity of the transverse process of the fourth vertebra and the clavicle. The 
inferior limb has but a slight forward inclination as it passes inwards to its 
articulation with the basioccipital. There are no post-temporal plates, nor is any 
portion of the inferior limb in contact with the anterior wall of the air-bladder. 
In shape the air-bladder (fig. 83) is a flattened cone, with its broad end directed 
forwards and firmly buttressed laterally by the anterior divisions of the modified trans- 
verse processes, and in the median line, though to a less extent, by the fan-shaped sub- 
vertebral process. In proportion to the size of the body, the bladder is fairly large. 
Internally, it is subdivided in the usual way by a T -shaped arrangement of the 
primary transverse and longitudinal septa. The transverse septum (t.s.) is rather 
