124 THE HUMAN BODY 



of smaller ones which are embedded wholly within the tongue. 

 These have no bony attachments at either end. 



In addition to its masticatory function (p. 469) the tongue is 

 an essential part of the speech apparatus. Its importance is shown 

 not only by the loss of the power of articulate speech from paralysis 

 or removal of the tongue, but also by the fact that only those lower 

 forms which have tongues at once fleshy and flexible (parrots, 

 tongue-cut crows) can learn to talk. The ape's tongue is very 

 similar to that of man. The fact that the parrot can learn to talk 

 while the ape cannot, or will not, raises the interesting question in 

 connection with the lower animals as to how much speech depends 

 on tongue-structure and how much on intelligence or willingness 

 to imitate sounds. The solution of this problem is a matter 

 for the student of animal behavior rather than for the physi- 

 ologist. 



Postures. The term posture is applied to those positions of 

 equilibrium of the Body which can be maintained for some time, 

 such as standing, sitting, or lying, compared with leaping, run- 

 ning, or falling. In all postures the condition of stability is that 

 the vertical line drawn through the center of gravity of the Body 

 shall fall within the basis of support afforded by objects with 

 which it is in contact; and the security of the posture is propor- 

 tionate to the extent of this base, for the wider it is the less is the 

 risk of the perpendicular through the center of gravity falling 

 outside of it on slight displacement. 



The Erect Posture. This is pre-eminently characteristic of 

 man, his whole skeleton being modified with reference to it. 

 Nevertheless the power of maintaining it is only slowly learnt 

 in the first years after birth, and for a long while it is unsafe. 

 And though finally we learn to stand erect without conscious 

 attention, the maintenance of that posture always requires the 

 co-operation of many muscles, co-ordinated by the nervous system. 

 The influence of the latter is shown by the fall which follows a 

 severe blow on the head, which may nevertheless have fractured 

 no bone nor injured any muscle: the concussion of the brain, as 

 we say, "stuns" the man, and until its effects have passed off 

 he cannot stand upright. In standing with the arms straight 

 by the sides and the feet together the center of gravity of the 

 whole adult Body lies in the articulation between the sacrum and 



