84 



pelvis is a vertebra in it. Its posterior C is sep- 

 arated from its anterior C by the diaphragm^ 

 which will be described further on. 



The head, neck, shoulder blades and this " com- 

 posite spine " may again be regarded as a com- 

 pound spine, of which the arms are the ribs. We 

 shall call this the hicomposite spine. The head, 

 taken with the shoulder blades, is a vertebra in it, 

 distinguished, however, from the pelvis as a ver- 

 tebra, in that while the " composite spine " gov- 

 erns the pelvis, the head governs the " bicomposite 

 spine." 



To some extent the arms act as ribs to the 

 composite spine ; also, and through them, the 

 head draws in a direct way on the hinder Hmbs.^ 



§ 85. Five vertebrce — two for each flexure, and one 

 for the point of contrary flexure — are the smallest 

 number of which an independent S curve could be 

 composed. If now, we alloiv one of each end for its 

 articulations with other points, we have seven verte- 



* Although the head be the " governour " and the spine the proper 

 " origin of all movement," movement may, in the higher animals, be 

 initiated in other parts. For example, a man in dropping from a 

 height may, by thrusting forward his hands or jerking back his elbows, 

 and thus changing the centre of gravity by altering the shape of the 

 body, through the medium of the breast-bone, change very materially 

 the point on which he alights from Avhat it would otherwise have been. 

 A horse in taking a fence, often does not know the ground on the far- 

 ther side, and no doubt while yet in air, he can, to some extent, deter- 

 mine his point of descent. 



