APPENDIX. 551 



bronchise which ramify into the lungs have not 

 the cartilages flat, but rather rounded ; a construc- 

 tion which admits of greater motion between each. 

 The pulmonary cells are smaller than in quadru- 

 peds, which may make less air necessary, and they 

 communicate with each other, which those of the 

 quadruped do not ; for by blowing into one branch 

 of the trachea, not only the part to which it im- 

 mediately goes but the whole lungs are filled. 



The parts immediately concerned in inspiration 

 are extremely strong ; the diaphragm remarkably 

 so. The reason of this must at once appear ; it 

 necessarily requiring great force to expand in a 

 dense medium like water, especially too when the 

 vacuity is to be filled with one which is rarer, 

 and is to water a species of vacuum, the pressure 

 being much greater on the external surface than 

 than the counter-pressure from within. But ex- 

 piration on the other hand must be much more 

 easily performed ; the natural elasticity of the 

 parts themselves, with the pressure of the water 

 on the external surface of the body, being greater 

 than the resistance of the air from within, will 

 both tend to produce expiration without any im- 

 mediate action of the muscles. 



The blow-hole or passage for air is next to 

 be described. As the nose in every animal that 

 breathes air is a common passage for the air, and 

 is also the organ of smelling, I shall describe it 

 in this tribe as instrumental to both those pur- 

 poses. 



