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 vertebrae in the former 

 instance being extremely thin and anchylosed together, and in the latter 

 greatly elongated. Reptiles possess only from three to eight cervical verte- 

 brae ; 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 vertebrae ; in fishes the ribs commence almost immedi- 

 ately behind the head. 



The views of Geoifroy de St. Hilaire, that nature in the organization of 

 the animal frame has caused the sternal portion to shift its position along the 

 vertebral column, seem to derive an important corroboration from the structure 

 of this animal ; but it is remarkable that whereas the sternum holds a mean 

 position in quadrupeds, and is thrown forward in fishes and backwards in 

 birds, yet its position in this instance assimilates the plesiosaurus less to 

 fishes, though destined to move in the same element f, than to birds, and 

 exhibits at the same time a very wide departure from the type of the Saurian 

 tribe. Although the number of the cervical vertebrae is thus unexampled, yet 

 the length of the neck is nearly rivalled by another of the reptile class, namely 

 the land tortoise. The length is in this case concealed by the anterior exten- 

 sion of the shell; the neck, however, notwithstanding its elongation, has only 

 eight vertebrae. The general proportions of the tortoise, its length of neck, 

 shortness of tail, and the smallness of its head, are in some degree analogous 

 to what we observe in the plesiosaurus ; but the structure of the head and 

 teeth of the latter, and its want of shell, entirely negative the idea of its being 



* The sparrow is said to possess only nine cervical vertebrjE. (Cuvier's Anatomie Comp.) In 

 aquatic birds the length of the neck, as well as the number of the cervical vertebras, generally 

 exceeds what we observe in the land birds, this construction enabling the former to procure sus- 

 tenatice in their own peculiar element. 



t The Testudo longicollis, an inhabitant of fresh water and a native of Australasia, [see Shaw's 

 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 the external appearance of this 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 vertebras. Most of the tortoise tribe have the power of extend, 

 ing 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. 



VOL. VI. 3 D 



