112 OF THE ANIMAL STRUCTURE 



ly, is not, as the thorax is by its ribs, reduced by natural 

 stays. It is evident, therefore, that the external proportion 

 does not arise from any equality in the shape or pressure 

 of the internal contents. What is it indeed but a correc- 

 tion of inequalities 1 an adjustment, by mutual compensa- 

 tion of anomalous forms into a regular congeries ? the ef- 

 fect, in a word, of artful, and, if we might be permitted so 

 to speak, of studied collocation ? 



3. Similar also to this, is the third observation ; that, 

 an, internal inequality in the feeding vessels is so managed, 

 as to produce no inequality in parts which were intended 

 to correspond. The right arm answers accurately to the 

 left, both in size and shape ; but the arterial branches, 

 which supply the two arms, do not go off from their trunk, 

 in a pair, in the same manner, at the same place, or at the 

 same angle. Under which want of similitude, it is very 

 difficult to conceive how the same quantity of blood should 

 be pushed through each artery ; yet the result is right : 

 the two limbs, which are nourished by them, perceive 

 no difference of supply, no effects of excess or deficien- 

 cy. 



Concerning the difference of manner, in which the sub- 

 clavian and carotid arteries, upon the different sides of 

 the body, separate themselves from the aorta, Chesselden 

 seems to have thought, that the advantage which the left 

 gain by going off at a much acuter angle than the right, 

 is made up to the right by their going off together in one 

 branch.* It is very possible that this may be the compen- 

 sating contrivance : and, if it be so, how curious, how hy- 

 drostatical ! 



II. Another perfection of the animal mass is the pack- 

 age. I know nothing which is so surprising. Examine 

 the contents of the trunk of any large animal. Take no- 

 tice how soft, how tender, how intricate they are ; how 

 constantly in action, how necessary to life. Reflect upon 

 the danger of any injury to their substance, any derange- 

 ment of their position, any obstruction to their office. Ob- 

 serve the heart pumping at the centre, at the rate of eighty 

 strokes in a minute : one set of pipes carrying the stream 

 away from it, another set, bringing, in its course, the fluid 

 back to it again : the lungs performing their elaborate of- 

 fice, viz. distending and contracting their many thousand 

 vesicles, by a reciprocation which cannot cease for a min- 



* Ches. Anat. p. 184. ed. 7. 



