34 ANIMALIA VERTEBRATA. 



the sides of the cavity of the trunk; they are articulated at 

 one extremity with the vertebrae, and most generally at the 

 other with the sternum; sometimes, however, they do not 

 encircle the trunk, and there are genera in which they are 

 hardly visible. 



There are never more than two pairs of members, but some- 

 times one or the other is wanting, or even both. Their forms 

 vary according to the movements they have to execute. The 

 superior members are converted into hands, feet, wings or 

 fins, and the inferior into feet or fins. 



The blood is always red, and appears to be so composed as 

 to sustain a peculiar energy of sentiment and muscular strength, 

 but in various degrees, corresponding to their quality of re- 

 spiration : from which originates the subdivision of the verte- 

 brata into four classes. 



The external senses are always five in number, and reside 

 in two eyes, two ears, two nostrils, the teguments of the 

 tongue, and those of the body, generally. In some species, 

 however, the eyes are obliterated. 



The nerves reach the medulla through the foramina of the 

 vertebrae or those of the cranium ; they all seem to unite with 

 this medulla, which, after crossing its filaments, spreads out 

 to form the various lobes of which the brain is composed, and 

 terminates in the two medullary arches called hemispheres, 

 whose volume is in proportion to the extent of the intelligence. 



There are always two jaws, the greatest motion is in the 

 lower one, which rises and falls; the upper jaw is sometimes 

 immovable. Both of these are almost always armed with 

 teeth, excrescences of a peculiar nature, which in their chemi- 

 cal composition are very similar to that of bone, but which 

 grow by layers and transudation ; one whole class, however, 

 that of birds, has the jaws invested with horn, and the genus 

 Testudo, in the class of reptiles, is in the same case. 



The intestinal canal traverses the body from the mouth to 

 the anus, experiencing various enlargements and contractions, 

 having appendages and receiving solvent fluids, one of which, 

 the saliva, is discharged into the mouth. The others, which 

 are poured into the intestine only, have various names : the 



