il* The Rev. W. D. Conybeare on the Discovery 



sal, which were placed before the humerus, and bore only five 

 ribs, fortj'-one*. This great inciease of the number of joints 

 in the neck is the more remarkable from the rigour with which 

 nature appears, in most cases, to have enforced the law of a 

 very limited number. In all quadrupedal animals, in all the 

 mammalia (excepting only the tridactyle slotlis, which have 

 nine) the series is exactly seven ; and so strict is the adiierence 

 to this rule, that even tlie short and stiff neck of the whale, 

 and the long and flexible neck of the cameleopard, 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 vertebrae ; birds, approaching in this 

 more nearly to the present species, but still falling greatly 

 short of it, have from nine to twenty-threef, the number being 

 the greatest in the swan. The Ichthi/osaurus appears to have 

 possessed about eighteen cervical vertebr£E. In fishes the ribs 

 commence almost immediately behind the head. 



The views of GeofFroy de St. Hilaire, — that nature in the or- 

 ganization of the animal frame has caused the stei'nal 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 Plesiosamiis less to fishes, though destined to move in the 

 same element:j:, than to birds, and exhibits at the same time 

 a very wide departure from the type of the Saurian tribe. Al- 



* It is difficult to assign the exact demarcation between these subdivi- 

 sions of the column; because the inferior lateral or hatchet-shaped pro- 

 cesses of the cervical vertebrae (which in this animal greatly resemble those 

 of the crocodile) gradually become elongated, and assume almost insensi- 

 bly the character of false ribs. 



f The sparrow is said to possess only nine cervical vertebrae (Cuvier's 

 Anatomic Comp.). In aquatic birds the length of the neck, as well as the 

 number of the cervical \'ertebrae, generally exceeds what we observe in the 

 land birds, this construction enabling the former to procure sustenance in 

 their own peculiar element. 



J The Tcstudo longicoUis, 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 Plcsiosaunis 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 vertebrae. 

 Most of the tortoise tribe have the power of extending their necks consi- 

 derably, especially the Testudoferox (see Shaw. vol. iii. p. 65), whose neck, 

 when exsertcd, is equal in length to the shell. By darting out this it is 

 enabled to make even birds its prey. 



though 



