THE DINOSAURIA. 
51 
The Crocodilian resemblance of the bones in Zanclodon is the 
more remarkable because in the Teleosaurs there is no such 
Crocodilian condition of the earliest neck vertebrae, hut a close 
resemblance to the same bones in Plesiosaurus. Here, then, as in 
the skull, there is evidence of evolution, in so far that in later 
time these joints of the neck acquire the characters seen in a 
higher organic type. The centrums or bodies of the vertebrae, 
both in the neck and hack, in many, if not all, of the older 
Dinosauria, have their articular surfaces flattened or concave ; 
and though this condition is retained in some of the latest 
known representatives of the group, such as the Dinosaurs of 
Grosau and of the Cambridge Greensand, many other genera, 
such as Megalosaurus and most of the Wealden types, have the 
bodies of the neck vertebrae convex in front and concavely- 
cupped behind, as among the ruminant mammals. This is the 
more interesting because the character was at first supposed to 
indicate a distinct genus, which was named Streptospondylus. 
It is probably one of the characters by which the Dinosauria 
will hereafter be divided into family groups. It is- especially 
remarkable, because no reptile presents the same modification, 
though the neck is so curiously constructed among Chelonians 
as to present this condition in one or two vertebrae. This 
reptilian resemblance is at least as strong and as important as 
that seen in the lower dorsal vertebrae of penguins, where the 
centrum is also opisthoccelous ; especially as the character becomes 
lost in the lower dorsal region of Dinosaurs. Consequently 
here, too, the change which the mode of union of the vertebrae 
presents is best explained as a condition of evolution going on 
within the group, by which, as ossification became more perfect, 
the neck vertebrae, like some of those of the back, put on a 
character that is only similarly developed among mammals. 
In all the Dinosauria the neck vertebrae have small, short ribs, 
with a double articulation, formed on the Crocodilian plan, 
(Fig. 4) ; and in the dorsal region the rib rises entirely on to 
the neural arch, and has two distinct articular faeets, the head 
joining the side of the neural arch, and the tubercle being 
connected with the transverse process (Fig. 5). In the older 
genera the dorsal vertebrae are moderately compressed from 
side to side, but in the newer types they often become more 
compressed, and the articulations for the rib rise higher up 
the neural arch, indicating an increased development of the 
lungs. The transverse platform of the neural arch in the 
region of the back, which is one of the distinctive characters 
of a Dinosaur, has a very bird- like appearance ; but it differs 
from that of the Crocodile chiefly in the transverse processes 
being relatively shorter, and lifted higher up the sides of the 
neural arch to make room for the lungs. Ho part of the 
