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suffer no inconvenience from a neglect of this precaution, whether it is 

 that, in them the vital power has more energy, and thus balances better 

 the law of mechanics, by opposing more powerfully the effects of gravi- 

 tation, or whether it is, that in very young children, the parietes of the 

 arteries within the skull, have a proportionate thickness, and consequently 

 greater power. The extreme disproportion observable in adults, in the 

 thickness of the parietes, between the cerebral arteries and those of other 

 parts of the body, is but trifling in children; and may not this difference 

 of structure, which I have several times observed in the course of dissec- 

 tion, be considered as one of the principal causes which, in old age, bring 

 on apopolexy, a disease to which the child is not liable? 



It is well known, that as the enlargement of the chest is produced by 

 the depression of the diaphragm, persons who have taken a plentiful 

 meal, dropsical patients, pregnant women, cannot rest, without lying on 

 a very inclined plane, so that the chest being considerably raised, and the 

 patient, as it were, seated, the weight of the abdominal viscera draws 

 them towards the most depending part, that their bulk may not interfere 

 with the depression of the diaphragm. 



We might now inquire what is the posture in which the body rests with 

 least fatigue : this investigation, unimportant to the physician, would be 

 of the highest value to the arts which have for their object the imitation 

 of Nature. In consequence of ignorance on this subject, we often see, in 

 the works of several of our sculptors, figures in attitudes of repose so in- 

 correct and uneasy, that they could not maintain them, without consider- 

 able effort and fatigue. 



CLXXXVII. Of the motions of progression. Of walking. Walking, 

 running, and leaping, are so closely connected, that it is difficult to dis- 

 tinguish them. There is, in fact, very little difference between walking, 

 in a certain manner, or running; and running is most frequently produced, 

 by the complicated mechanism of running and leaping. In the most na- 

 tural way of walking, we, in the first instance, poise the body on one 

 foot, then, bending the opposite foot on the leg, the latter on the thigh, 

 and the thigh on the pelvis, we shorten that extremity; we, at the same 

 time, carry it forward, extend its articulations which are bent, and when 

 firmly applied to the ground, we bend the body forward, and carry back 

 the centre of gravity in that direction; and performing the same motions 

 with the limb which remained behind, we measure the space the more 

 rapidly, cseteris paribus, as the levers of which the centre of the gravity 

 alternately bears, are longer. The weight of the body, compared to that 

 of the lower extremities, is as that of a carriage which moves, in succes- 

 sion, on the different spokes of its wheels. 



The centre of gravity does not move along a straight line, but between 

 two parallels, in which space it describes oblique lines from the one pa- 

 rallel to the other, and forms zig zags. The oblique direction of the neck 

 of the thighbones, accounts for the lateral oscillations of the body, when 

 we walk ; the arms which move, in a different direction, from that of the 

 lower extremities, serve to balance us, preserve the equilibrium, and cor- 

 rect the staggering, which would be much greater, if the neck of the 

 thigh bone., instead of being oblique, had been horizontal. The impulses 

 communicated to the trunk, are reciprocally balanced, and the latter 

 moves in the diagonal of a parallelogram, whose sides are represented by 

 the line of these impulses. We constantly deviate from the straight line, 



