128 COMPARATIVE AN'ATOMY. 



But under the present division of our subject, our busi- 

 ness with feathers is, as they are the covering of the bird. 

 And herein a singular circumstance occurs. In the small 

 order of birds which winter with us, from a snipe down- 

 wards, let the external colour of the feathers be what it 

 will, their Creator has universally given them a bed of 

 black down next their bodies. Black, we know, is the 

 warmest colour : and the purpose here is, to keep in the 

 heat, arising from the heart and circulation of the blood. 

 It is further likewise remarkable, that this is not found in 

 larger birds; for which there is also a reason. Small birds 

 are much more exposed to the cold than large ones; foras- 

 much as they present in proportion to their bulk, a much 

 larger surface to the air. If a turkey was 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 bo more warmly clad than large ones, and this 

 seems to be the expedient, by which that exigency is pro- 

 vided 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 conve- 

 niency, than that which is seen in the different formations 

 of their moutlis. Whether the purpose be the reception of 

 aliment merely, or the catching of prey, the picking up 

 of seeds, the cropping of herbage, the extraction of juices, 

 the suction of liquids, the breaking and grinding of food, 

 the taste of that food, together with the respiration of air, 

 and in conjunction with the utterance of sound ; these 

 various offices are assigned to this one part, and, in differ- 

 ent species, provided for, as they are wanted, by its differ- 

 ent constitution. In the human species, forasmuch as 

 there are hands to convey the food to the mouth, the mouth 

 is flat, and by reason of its flatness fitted only for recep- 

 tion : whereas the projecting jaws, the wide rictus, the 

 pointed teeth, of the dog and his affinities, enable them to 

 apply their mouths to snatch and 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 broics- 

 ing upon their pasture ; either gathering large mouthfuls 



