ATTITUDES STANDING. 437 



ATTITUDES. 



The attitudes, which man is capable of assuming, are of different 

 kinds. They may, however, be reduced to two classes the active and 

 the passive; the former including those that require a muscular effort; 

 and the latter comprising only one variety, that in which the body is 

 extended horizontally on the soil, and no effort needed to maintain its 

 position. 



We shall begin with the most ordinary attitude ; that of standing 

 on both feet. This requires considerable muscular effort to preserve 

 equilibrium. The base of sustentation the space comprised between 

 the feet plus that occupied by the feet themselves is small ; whilst the 

 centre of gravity is high. The body, again, does not consist simply 

 of one bone, but of many; all of which have to be kept steady by 

 muscular effort; and it is necessary, Jhat the vertical line shall fall 

 within the base of sustentation, in order that equilibrium may be pre- 

 served. 



That standing is the effect of the action of the different extensors 

 is proved by the fact, that if an animal be killed suddenly, or stunned, 

 so that volition is no longer exerted over the extensors, it immediately 

 falls forward. 



The head, which is intimately united with the atlas or first vertebra 

 of the neck, forms with it a lever of the first kind; the fulcrum being 

 in the articulation of the lateral parts of the atlas and vertebra dentata; 

 whilst the power and the resistance occupy the extremities of the lever; 

 and are situate the one at the face, the other at the occiput. The ful- 

 crum being nearer the occiput than to the anterior part of the face, the 

 head has a tendency to fall forwards. This can be readily seen by sup- 

 porting a skull on the condyles; yet Mr. Abernethy 1 affirms, that "the 

 condyles are placed so exactly parallel in the centre of gravity, that 

 when we sit upright, and go to sleep in that posture, the weight of the 

 head has a tendency to preponderate equally in every direction, as we 

 see in those who are dozing in a carriage"! In the living subject, the 

 preponderance anteriorly is not so great as it is in the skeleton, because 

 the greater part of the encephalon is lodged in the posterior portion; 

 but the fact, that when we go to sleep in the upright position the head 

 drops forward is sufficient evidence that it exists; and that in the waking 

 state the head is kept in equilibrium on the vertebral column by the 

 contraction of the extensor muscles of the head, which are situate at 

 the back part of the neck, and inserted into the head; as the splenius, 

 complexus, trapezius, and posterior recti. These muscles are inserted 

 perpendicularly into the lever or bone to be moved, an advantage, 

 and some compensation for the shortness of the arm of the lever by 

 which they act. 



In quadrupeds, the head not being in equilibrium on the spine these 

 muscles are large and strong; the spinous and transverse processes of 

 the vertebrae and the occipital depressions are larger; and, in addition, 



1 Physiological Lectures, exhibiting a general view of Mr. Hunter's Physiology, &c., 

 Lect. 3, 2d edit., p. 115, London, 1822. 



