CIIELOMA. 2G9 



The Saurians (or Lizards), which liave a heart with two auricles, and the hody of 

 which, borne on four or two feet, is covered with scales. 



The OrniDiANS (or Serpents), having a heart with two auricles, and the body of 

 wdiich is always deprived of feet. And 



The Batrachians, the heart of which has only one auricle; [Prof. Owen has 

 shown that these also possess twoj ; and which have a naked body, that in the greater 

 number passes, vi-ith age, from the form of a Fish respiring by gills, to that of a 

 Quadruped breathing by lungs. Some of them, however, never cast their gills; and 

 there are certain species which have only two feet. 



Other authors, as iVIerrcm, have made a different partition of the Saurians and 

 Ophidians. They detach the Crocodiles to form an order [Loricata] by themselves, 

 and place the rest of the Saurians with the first family of Ophidians (or that of the 

 Orvets), which mode of distribution is founded on certain peculiarities of the organiza- 

 tion of the Crocodiles, and upon a certain affinity of the Orvets for the Lizards. We 

 have deemed it sufficient to indicate these affinities, which are nearly all internal, 

 adopting, nevertheless, a division of more easy application. [In consequence, how- 

 ever, of rejecting this obvious natural arrangement, the Ophidians and Saurians of 

 our author grade into each other ; whereas the more intrlnsical characters remain 

 inviolate, and indicate three natural groups of Loricuta, Saurophidia, and Ophkliu.~\ 



THE FIRST ORDER OF REPTILES, 



chelonia,- 



Bettcr known by the apjiellation of Tortoises iTestudinrita]. have a heart with two auricles, 

 and a veutricle with two unequal chambers, which eounnuiiicate together. The blood from 

 the body enters the right auricle, and that from the lung the left ; but the two streams mingle 

 more or less in passing through the ventricle. 



These aniaials are distinginshed, at the first glance, by the double buckler in which their 

 body is inclosed, and which only allows the head and neck, the tail, and the four lindis, to be 

 protruded. 



The u]ipcr l)uckler, termed the carapace or shield, is formed by the ribs, in numljer eight 

 pairs, which are widened and joined together, and also to tlie plates adhering to the annular 

 portion of the dorsal vertebra?, by dentelated sutures, so that the whole is completely de])rived of 

 mobdity. Tlie inferior buckler, named the plastron or breast-])latc, is formed ot pieces which 

 represent the sternum, and which are ordinardy nine in number. A frame-work composed of 

 bonv ]neces, which are believed to have some analogy to the sternal or cartilaginous portion 

 of ribs, and which in one subgenus even remains cartilaginous, surrounds the carapace, and 

 unites all the ribs which compose it. The cervical and caudal vertebra are alone moveable. 



These two bony envelopes are immediately covered by the skin, or by scales; the scapula, 

 and all the muscles of the arm and neck, instead of being attached to the ribs and spine, as 

 111 other animals, arc all underneath, as are also even the bones of the pelvis and all the muscles of 

 the thigh ; so that, in this respect, a Tortoise may be regarded as an animal turned inside-ont. 



The vertebral extremity of the blade-bone is articulated to the carapace ; and its opposite 

 extremity, which may be considered as analogous to a clavicle, is articulated to the breast- 

 plate ; so that the two shoulders form a ring, through wdiich jmss the tesopbagus and trachea. 



