VERTEBRAL ANIMALS. 165 



ternally with appendices, or internally with a layer of fat, to 

 act as non-conductors of the heat which is generated. The 

 regulation of the temperature, to suit the varying external 

 circumstances, is effected by the quantity produced, by the 

 quantity or colour of the non-conducting substances, regu- 

 lating its escape by transmission or radiation. 



The presence of ribs, and a sternum, for the protection 

 of the cavity containing the viscera, is universal. The an- 

 terior extremity is likewise furnished with scapular and 

 clavicular bones. The muscles contain a greater quantity 

 of fibrin than in the other classes. The brain occupies the 

 whole cavity of the skull, and exhibits several markings on 

 its surface *. The eyes are furnished with eye-lids. The 

 passage of the nose communicates with the windpipe. The 

 cochlea of the ear is present. In many species, whiskers or 

 long hairs are placed about the mouth. The intestinal ca- 

 nal is distinguished into small and great guts^ and supplied 

 with gastric, pancreatic, and biliary glands. 



The heart is double, and the circulation is complete. 

 All the blood must pass through the lungs before entering 

 the systemic heart, to be distributed through the aorta to 

 the body. Free air is respired through a windpipe fur- 

 nished with a larynx. The lungs are double. The sexes 

 are uniformly separate, on different individuals, and inter- 

 nal fecundation is requisite. 



The warm blooded animals are divided into Quadrupeds 

 and Birds. 



QUADRUPEDS. 



Char. Ovarium double. 



Des. The appendices of the skin of quadrupeds consist 

 either of hair or scales, and differ remarkably from the 



Vol. i. ib. 



