ISiti THE ANATOMY OF VERTEBRATED ANIMALS. 



of the dorsal vertebrae and ribs are restrained from motion by the 

 union of superficial bony plates, into which they pass, to form a 

 citrapare. 



Dermal bones, usually nine in number, one of which is median and 

 symmetrical, and the others lateral and paired, are developed in the 

 ventral "alls of the thorax and abdomen, forming a, plastron. 



I. — Cheloiiiir. 

 B. The dorsal vertebra; (which haveeither complete, or rudimentary, 

 transverse processes), are moveable upon one another, and the ribs 

 upon them. There is no plastron. 



a. The dorsal vertebra; have transverse processes, which are 



either entire, or only very imperfectly divided into terminal 

 facets ( Erpetoxpoudylia). 



a. The transverse processes are long ; tlie limbs well developed, 



with the digits united by the integument into a paddle ; the 

 sternum and sternal ribs are absent or rudimentary. 



II, — Plesiosatiria. 



b. The transverse processes are short, and sometimes rudi- 



mentary ; the limbs present or absent ; when they are fully 

 developed, the digits arc free, and there is a well-developeil 

 sternum with sternal ribs. 



a. A pectoral arch and urinary bladder. 



III. — Lacertilia. 

 h. Tso pectoral arch, and no uiinary bladder. 

 W .— Opkidia. 



b. The dorsal vertebra; have double tubercles in the place of 



transvei-se processes {PeroaponflyUa). The limbs are paddle- 

 like. 



V. — Tchthi/osavria. 



c. The anterior dorsal vertebra have elongated and divided trans- 



verse processes, the tubercular being longer than the capitular 

 division {Sur/iospondi/lia) . 

 a. With only two vertebra; in the sacrum. 



VI. — Crocodilia . 

 it. With more than two vertebra: in the sacrum. 

 (/. Tie manus without a prolonged ulnar digit. 

 1. The hind limb saurian. 



VII. — Dicynodont'ia. 



'1. The hind limb ornithic. 



\ III. — Ornithofcelida. 



h. Tlie manus having an extremely prolonged ulnar digit. 



\^--Pterosauria, 



I shiill describe the exoskeletal. endo skeletal, and dental 

 systems of the chief groups of the Beptilia, under the 

 s(M(n-al heads here enumerated, and I shall then <A\e an 



