|an almost perfect Skeleton of the Plesiosaurus||383|
mammalia (excepting only the tridactyl sloths
which have nine), the series is exactly seven ; and so strict is the
adherence to this rule, that even the short and stiff neck of the
whale, and the long and flexible neck of the camelopard, are formed
out of the same elementary number; the vertebræ in the former
instance being extremely thin and anchylosed together, and in the
latter greatly elongated. Reptiles possess only from three to eight
cervical vertebra ; birds, approaching in this more nearly to the
present species, but still falling greatly short of it, have from
nine to twenty-three*, the number being the greatest in the swan.
The ichthyosaurus appears to have possessed about eighteen cervical
vertebræ; in fishes the ribs commence almost immediately
behind the head.
|* The sparrow is said to possess only nine
cervical vertebra;. (Cuvier's Anatomic Cornp.) In aquatic
birds the length of the neck, as well as the number of the cervical
vertebræ, generally exceeds what we observe in the land birds,
this construction enabling the former to procure sustenance in their
own peculiar element,
The Testudo longicollis, an inhabitant of fresh water and a native of Australasia, [see Shaw1' Zoology, Vol. III. p. 62.] is the most remarkable among the tortoises for length of neck ; and the figure of this animal in the work referred to, will serve to illustrate what in the Plesiosaurus must have been (he external appearance of (his part when covered with integuments. It would be very desirable to ascertain, from an examination of the skeleton, whether this species has more than the usual number of cervical vertebræ. Most of the tortoise tribe have the power of extending their necks considerably ; especially the Testudo ferox, [see Shaw, Vol.III. p. 65.]whose neck, when exserted, is equal in length to the shell. By darting out this it is enabled to make even birds its prey.