PLESIOSAURUS. 205 
Neck, 
The most anomalous of all the characters of 
P. Dolichodeirus is the extraordinary extension 
of the neck, to a length almost equalling that of 
the body and tail together, and surpassing in the 
number 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 
seum, of which the entire figure, on a smaller scale, is given in 
PI. 16. The head is in a supine position ; the upper jaw is dis- 
torted, and shows several of the separate alveoli that contained 
the 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 PL 18, Fig. 1, taken 
from a specimen also in the British Museum, found by Mr. Haw- 
kins, at Street. 
PI. 19, Fig. 3, represents the extremity of the dental bone of 
another lower jaw, in the same collection, retaining several teeth 
in the anterior sockets, and also exhibiting a series of new teeth, 
rising 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, 
combined with the position of the perfect teeth in distinct alveoli, 
after the manner of Crocodiles. 
The number of teeth in the lower jaw was fifty-four, which, if 
met by a corresponding series in the upper jaw, must have made 
the total number to exceed one hundred. The anterior part of 
the extremity of the jaw enlarges itself like the bowl of a spoon, 
to allow space for the reception of the six first teeth on each side, 
which are the largest of all. 
