VERTEBRATA. 19 



middle and index fingers have each two phalanges, the others 

 three. 



The posterior extremity, for reasons before assigned, reaches a 

 high degree of development. The cotyloid cavity is constituted by the 

 ilium, ischium, and pubis. The femur is long and cylindrical. The 

 tibia and fibula are consolidated into one bone, and joined inferiorly 

 to two bones representing astragalus and os calcis. Between these 

 and the long metatarsal bones are placed four small, irregular 

 bones. Of the rive toes, the internal is best developed, and sus- 

 tains three long, slender phalanges. 



The structure and form of the salamander, proteus, and siren, 

 are well contrasted with those of the froo\ In the former animals, 

 the spinal column attains a high state of development : the extre- 

 mities are reduced to a rudi mental type. The bones of the fore- 

 arm and leg, instead of being anchylosed as in the frog, maintain 

 a permanent state of separation. The toes, which are four in 

 number, are but slightly developed. The whole economy of the 

 frog is admirably organised for rapid terrestrial progression, while 

 that of the other animals is designed to favour their movements 

 through a watery element. 



Who can fail to observe the extreme wisdom manifested in the 

 metamorphosis of these animals? In the early part of their exist- 

 ence, and while they enjoy an aquatic mode of life, their organi- 

 sation is in due accordance ; at first their members are scarcely 

 perceptible, whilst their tail is of great length, and continues so in 

 those destined to continue their watery habitation ; but in the frog, 

 (fee, which are to breathe by lungs, the tail is gradually removed 

 by absorption, and the extremities, particularly the posterior, un- 

 dergo a rapid evolution. 



REPTILIA. 



Chelonia.—These reptiles present a tolerably perfect form of ske- 

 leton. Their spine consists of eight cervical, fourteen dorsal, three 

 sacral, and from twenty to thirty caudal vertebrae. There are 

 eight pairs of immovable ribs, united to each other by sutures, and 

 attached between the bodies of the vertebrae. By the union of the 

 ribs with each other, and with the spinous processes of the dorsal 

 vertebras, they form the upper shield or carapace. The nine pieces 

 of the sternum which are movable in the turtle, form the lower 

 shield or plastron. This unyielding frame-work is well suited to 

 resist pressure, as well as to favour their muscular movements on 

 land, whilst the mobility of the several elements of the sternum in 

 the aquatic species is applicable to their extensive respiration in that 

 dense element. 



The bones of the head are firmly united by sutures. The occi- 

 pital condyle presents three facets, formed by the basilar and the 

 two condyloid portions. The inter-maxillary bones are narrow, 

 but present a large palatine surface. The bones of the ear are 



