PLESIOSAUKUS. 
205 
Neck. 
The most anomalous of all the characters of 
F*. Dolichodeirus is the extraordinary extension 
of the neck, to a length almost equalling that of 
Hie body and tail together, and surpassing in the 
Humber of its vertebrae (about thirty-three) that 
of the most long-necked bird, the Swan : it thus 
deviates in the greatest degree from the almost 
seurn, of which the entire figure, on a smaller scale, is given in 
Hi. 16. The head is in a supine position; the upper jaw is dis- 
torted, and shows several of the separate alveoli that contained 
tile teeth, and also the posterior portion of the palate. The 
under jaw is but little disturbed. 
A figure of another lower jaw is given at PI. 18, Fig. 1, taken 
from a specimen also in the British Museum, found by Mr. Haw- 
l^ins, at Street. 
Pi. 19, Fig. 3, represents the extremity of the dental bone of 
another lower jaw, in the same collection, retaining several teeth 
m the anterior sockets, and also exhibiting a series of new teeth, 
Using within an interior range of small cavities. This arrange- 
ment for the formation of new teeth, in cells within the bony 
mass that contains the older teeth, from which they shoot irre- 
gularly forwards through the substance of the bone, forms an 
important point of resemblance whereby the Plesiosaurus as- 
sumes, in the renovation of its teeth, the character of Lizards, 
mimbined with the position of the perfect teeth in distinct alveoli, 
ufter the manner of Crocodiles. 
Pile number of teeth in the lower jaw was fifty-four, which, if 
Uiut by a corresponding series in the upper jaw, must have made 
IS total number to exceed one hundred. The anterior part of 
s extremity of the jaw enlarges itself like the bowl of a spoon, 
lo allow space for the reception of the six first teeth on each side, 
which 
are the largest of all. 
