REPTILIA. 



265 



but varies with the proportion which the 

 diameter of the pulmonary artery bears to 

 that of the aorta. From this proceed diffe- 

 rences of energy and sensibility much greater 

 than can exist between one mammiferous 

 animal and another, or one bird and another. 



Accordingly, the reptiles exhibit forms, 

 movements, and properties much more various 

 than the two preceding classes ; and it is 

 more especially in their production that nature 

 seems to have sported in the formation of 

 fantastic shapes, and to have modified in all 

 possible ways the general plan which she has 

 followed for vertebrated animals. 



The comparison of their quantity of respi- 

 ration and their organs of motion has, how- 

 ever, given foundation for their separation 

 into three distinct orders, viz. : 



1st, The CHELONIANS, or TORTOISES (Che- 

 Ionia), in which the body, supported on four 

 legs, is enveloped by two plates or shields, 

 formed by the ribs and the sternum. 



2d, The SAURIANS, or LIZARDS (Sauria), 

 in which the body, supported on four or on 

 two feet, is covered with scales. 



3d, The OPHIDIANS, or SERPENTS (Ophi- 

 dia), in which the body is always destitute of 

 limbs. 



ORDER i. CHELONIA. 

 Family 1. TESTUDINID.E. 



Testudo (Land Tortoise), Emys (Fresh- 

 water Tortoise), Chelonia (Turtle), 

 Chelys, Trionyx. 



ORDER II. SAURIA.* 



Family 1. CROCODILID.E. 

 Gavial, Crocodilus, Alligator. 



Family 2. LACEUTIDJE. 

 Monitor, Crocodilurus, Tupinambis, Ame- 

 iva, Lacerta, Algyra, Tachydromus. 



Family 3. IGUANID;E. 

 Stellio, Cordyliis, Stcllio, Doryphorus, Uro- 

 mastiv, Agama, Agama, Tapayes, Tra- 

 pclits, Leio/epis, Tropidolepis, Leposoma, 

 Cahtes, Lophyrus, Gonocephalus, Lyrio- 

 cephahis, Brachylophiis, Pkysignatkus, Is- 

 tiuru.s, Draco, Sitana, Iguana, Ophryessa, 

 Basiliscus, Polychrus, Ecphimotes, Opiu- 

 ms, Anolius. 



Family 4. GECKOTID^E. 

 Gecko, Platydactylus, Hemidactylus, Theca- 

 dactylus, Ptyodactylus, Spheriodactylus, 

 Stenodactylus, Gymnodactylus, Pliyllunts. 



Family 5. CHAMTELEONIDJE. 

 Charnaeleo. 



Family 6. SCINCID./E. 

 Scincus, Seps, Bipes, Chalcides, Chirotes. 



ORDER III. OPHIDIA.f 



Family 1 . AN GU I D,E. 

 Anguis, Pseudo2)its, Ophisaurus, Angnis, 



Acontias. 



traufe;, a lizard. 

 Sfnt a serpent. 



Family 2. SERPENTIDTE. 



Amphisbffina, Typhlops, Tortrix, Boa 

 Scytalits, Eryx, Erpcton, Coluber, Py- 

 ihon, Cerberus, Xenopcltis, Heterodon, 

 Hurria, D'tpsas, Dendrophis, Dryinus, 

 JDryophi/s, Oligodon, Acrochordus, Cro- 

 talus, Trigonocephalus, Vipera, Naia, 

 Elaps, Micrurus, Platurus, Trimeresurus, 

 Oplocephalits, Acanthophis, Echis, Lan- 

 gafia, Bongarus, Hydrus, Hydrophis, Pe- 

 lamidcs, Chersydrus. 



Family 3. CJECILIAD^:. 

 Cascilia. 



Osteology. The Chelonian reptiles are 

 distinguished from all other vertebrata by 

 the peculiar construction of their skeleton ; 

 the bones of the thorax being in these re- 

 markable animals literally placed externally 

 so as to form a suit of armour that encloses 

 the muscles as well as the viscera, and within 

 which the bones both of the shoulder and of 

 the pelvis are lodged. The greater part of 

 the dorsal shield or carapax is formed by- 

 eight pairs of ribs (fg. 177, i) united to each 

 other towards the mesial line by a longitudinal 

 series of angular plates, which are in fact the 

 spinous processes (ne ural spines) of as many 

 vertebrae spread out horizontally. The ribs 

 are connected by suture to the margins of 

 these plates, and likewise to each other, either 

 along their whole length, or to a greater or 

 less extent, according to the species or the 

 age of the animal. 



In front of the carapax there are eight 

 vertebrae which do not enter into its compo- 

 sition (fg. 177, E) : of these the seven anterior 

 ones, which are ordinary cervical vertebrae, 

 are quite free in their movements. The eighth 

 vertebra, which may be called the first dorsal, 

 is placed obliquely between the last moveable 

 cervical and the first vertebra entering into 

 the composition of the carapax ; posteriorly 

 this vertebra (the eighth) has its spinous 

 process somewhat elongated and slightly en- 

 larged, for the purpose of its attachment by 

 synchondrosis to a tubercle that is situated 

 upon the lower surface of the first of the 

 series of the mesian plates of the carapax. 



The ribs which, by their external broad 

 plates, enter into the composition of the ca- 

 rapax, give off from their inferior surfaces a 

 process which corresponds with what in ordi- 

 nary skeletons is called the head of the rib. 

 This process is always connected with the 

 spine between the bodies of two contiguous 

 vertebrae, as are the heads of the ribs in other 

 animals ; and, carrying out the comparison, 

 that part of the ribs which articulates by 

 suture with the median plate may be regarded 

 as the " tubercle," only here it is connected 

 with the expanded spinous process instead of 

 the transverse. 



In the Turtles the ribs are not united to 

 each other throughout their whole length; 

 towards their external extremities there only 

 remains the narrow central portion, the inter- 

 vals between the contiguous ribs being in this 



