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 vertebræ (about thirty-three)
that of the most long-necked bird, the Swan: it thus deviates
in the greatest degree from the almost universal law,
which limits the cervical vertebræ of quadrupeds to a very
small number. Even in the Camelopard. the Camel, and
Lama, their number is uniformly seven. In the short neck
of the Cetacea the type of this number is maintained. In
Birds it varies from nine to twenty-three; and in living
Reptiles from three to eight.[1] We shall presently find in
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.
- ↑ To compensate for the weakness that would have attended this great elongation of the neck, the Plesiosaurus had an addition of a series of hatchet-haped processes, on each side of the lower part of the cervical vertebrae. (Pl. 17, and Pl. 19, 1, 2.) Rudiments and modifications of these processes exist in birds, and in long-necked quadrupeds. In the Crocodiles they assume a form, most nearly approaching that which they bear in the Plesiosaurus.
The bodies of the vertebræ also more nearly resemble those of certain fossil Crocodiles, than of Ichthyosauri or Lizards; they agree further with the Crocodile, in having the annular part attached to the body by sutures; so that we have in the neck of the P. Dolichodeirus a principle of construction resembling that of the vertebrae of Crocodiles; combined with an elongation very much exceeding that of the longest neck in birds, and such as occurs in no other known animal of the extinct or living creations. The length of the neck in P. Dolichodeirus is nearly five times that of the head; that of the trunk four times the length of the head, and of the tail three times; the head itself being one-thirteenth part of the whole body.—See Geol. Trans. Lond. Vol. 5, p. 559, and Vol. I. N. S. p. 103, et seq.
