90 SKELETON 



it erect, have their insertion so much in the line of motion, that 

 they perform their part very imperfectly, and the spine is con- 

 tinually bending forwards, from the erect position. All the 

 transverse processes are also imperfectly developed, those of 

 the loins are particularly deficient; those of the thorax and neck 

 are less deficient; as in the one case they have to form an arti- 

 cular surface for the ribs, and in the other to allow passage to 

 the vertebral artery. The bodies of the vertebrae are. imper- 

 fectly ossified, and are separated by cartilage from the processes. 

 The epiphyses, or upper and lower surfaces of the bodies, are 

 in the state of cartilage: the bodies, therefore, are rounded both 

 above and below, whereby their surfaces of contact are much 

 reduced in extent, and the line of support to the trunk rendered 

 much less firm. When, at this age, the vertebras are macerated, 

 their bodies present themselves as small rounded tubercles; and 

 very nearly one-half the whole length of the spine is made up 

 of the cartilaginous epiphyses and the inter-vertebral cartilages- 

 The spine, in the foetus, is almost straight, and scarcely presents 

 at all those curvatures, for which it is so remarkable in adult 

 life. This depends upon the rounded form of the bodies of the 

 vertebra3, and the sameness of thickness in the inter-vertebral 

 matter at its anterior and posterior edge. 



SECT. III. ON THE USES OF THE VERTEBRAL COLUMN.. 



The vertebral column performs three important offices in the 

 animal economy. It affords a secure lodgement to the spinal 

 marrow; is a line of support to the trunk, in every variety of 

 position;'and is the centre of all its movements. 



In standing, the spine also supports the head, which it can 

 do very conveniently, from the horizontal direction of the con- 

 dyles and their nearly central position on the occiput, and from 

 the head being almost in equilibrium when we stand erect. The 

 volume of the head is so much greater before the condyles than 

 behind them, that upon a superficial view one would suppose its 

 preponderance in front to be very considerable. This is, how- 

 ever, less than it might seem to be, for two reasons: one is, that 

 the diameters of the head are augmented behind the condyles, 

 and, secondly, it is formed of solid matter; whereas, in front 

 a great deal of it is hollow, for the construction of the nose and 



