200 
MARINE SAURIANS. 
universal law, wliich limits the cervical vertebrae 
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 main- 
tained. In Birds it varies from nine to twenty- 
three ; and in living Reptiles from three to eight.* 
We shall presently find in the habits of the 
Plesiosaurus a probable cause for this extraordi- 
nary deviation from the normal character of 
the Lizards. 
• 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-shaped processes, on each side 
of the lower part of the cervical vertebrae. (PI. 17, and PI. 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 vertebrae also more nearly resemble those 
of certain fossil Crocodiles, than of Ichthyosauri or Lizard.s; 
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 vertebrse 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-thir- 
teenth part of the whole body.— See Geol. Trans. Lond. Vol. 5, 
p. 559, and Vol. I. N. S. p. 103, et seq. 
