COMPARATIVE ANATOMY. 149 



present, in proportion to their bulk, a much larger surface 

 to the air. If a turkey were divided into a number of 

 wrens — supposing the shape of the turkey and the wren to 

 be similar — the surface of all the wrens would exceed the 

 surface of the turkey in the proportion of the length, breadth, 

 or of any homologous line, of a turkey to that of a wren, 

 which would be, perhaps, a proportion of ten to one. It 

 was necessary, therefore, that small birds should be more 

 warmly clad than large ones ; and this seems to be the ex- 

 pedient by which that exigency is provided for. 



II. In comparing different animals, I know no part of 

 their structure which exhibits greater variety, or, in that 

 variety, a nicer accommodation to their respective conven- 

 iency than that which is seen in the different formations of 

 their mouths. Whether the purpose be the reception of ali- 

 ment merely, or the catching of prey, the picking up of seeds, 

 the cropping of herbage, the extraction of juices, the suction 

 of hquids, the breaking and grinding of food, the taste ol 

 that food, together with the respiration of air, and in con- 

 junction with it, the utterance of sound, these various offi- 

 ces are assigned to this one part, and, in different species, 

 provided for as they are wanted by its different constitution. 

 In the human species, forasmuch as there are hands to con- 

 vey the food to the mouth, the mouth is flat, and by reason 

 of its flatness, fitted only for reception; whereas the pro- 

 jecting jaws, the wide rictus, the pointed teeth of the dog 

 and his affinities, enable them to apply their mouths to 

 snatch a7id seize the objects of their pursuit. The full lips, 

 the rough tongue, the corrugated cartilaginous palate, the 

 broad cutting teeth of the ox, the deer, the horse, and the 

 sheep, qualify this tribe for browsing upon their pasture : 

 either gathering large mouthfuls at once, where the grass ih 

 long, which is the case with the ox in particular, or biting 

 close where it is short, which the horse and the sheep are able 

 to do in a degree that one could hardly expect. The retir- 

 ed under-jaw of the swine works in the ground, after the 



