22 SKELETON. MOVEMENT. 



4. The skeleton in reptiles is composed of almost the same 

 bones as those we have already seen in mammals and birds r 

 but it often happens that some among them are entirely wanting : 

 serpents, for example, have no extremities, nor have they any 

 sternum ; and frogs have no ribs. 



5. The head, in the arrangement of its" bones, resembles that 

 of birds more than that of mammals ; the cranium is small ; the 

 fare is generally much elongated, and the lower jaw is suspended 

 from a tympanic bone, which is placed between it and the cranium. 

 In general, the head is articulated with the vertebral column 

 by a single tubercle (or condyle,) which has many facettes, and 

 possesses only very slight mobility. 



6. The structure of the vertebral column differs extremely in 

 the different reptiles : in serpents it is very long and very flexi- 

 ble ; in frogs it is very short and slightly moveable ; and in tor- 

 toises its middle part is united so as to form a single bony piece. 



7. Generally, the ribs are very numerous ; in serpents, they 

 exist through almost the entire length of the body ; the same is 

 the case in certain reptiles resembling lizards, while in others, 

 these bones are merely rudimentary, or entirely wanting. In 

 tortoises, they are soldered, as it were, to each other ; and with the 

 dorsal portion of the vertebral column, form the great shield or 

 buckler which covers the backs of these animals, and which is 

 called carapax. 



8. Without being as much developed, the bones of the shoulder 

 are very analogous to those of birds. The anterior extremity 

 consists of an arm composed of a single bone, the humerus ; a 

 fore-arm consisting of a radius and ulna, generally distinct from 

 each other, and a hand which is sometimes in the form of a fin, 

 and sometimes resembling a foot. 



9. The movements of reptiles, are, in general, less active, and 

 less sustained than those of animals with warm blood, as might 

 be anticipated from the more limited character of their respira- 

 tion; for there always exists an intimate relation between these 

 two functions. Their muscles receive less blood, and are of a 

 whitish tint; and it is also remarked that these organs preserve their 

 irritability for a longer time after they have been removed from the 

 influence of the nervous system.' In warm-blooded animals, the 



4. What is the character of the skeleton in Reptiles? 



5. What is the general character of the head in Reptiles ? 



6. Is the structure of the vertebral column the same in all Reptiles ? 



7. What is the character of the ribs in Reptiles ? 



8. What is the character of the anterior extremity of Reptiles? 



9. Why are the motions of Reptiles less active than those of mammals 

 and birds ? What are the characters of the muscles of Reptiles ? 



