MOVEMENTS. 443 



MOVEMENTS. 



The movements, of which the body is susceptible, are of two kinds, 

 partial and locomotive; the former simply changing the relative situa- 

 tion of parts of the body; the latter the relation of the whole body 

 to the soil. Many of the partial movements constitute an inherent part 

 of the different functions, and are considered under them. 



In the erect attitude, whilst the body holds the same correspondence 

 with the soil, the position of the upper parts of the body may be greatly 

 varied, provided the vertical line falls within the base of sustentation. 

 Accordingly, to produce this effect, if the upper part of the body be 

 inclined in one direction, the lower will have to be thrown more to the 

 opposite. 



The head may be turned forwards, backwards, or to one side ; and 

 it is capable of a rotatory motion to the right and left. The three first 

 movements, when slight, occur in the articulation of the occipital bone 

 and atlas ; but if to a greater extent, the whole of the cervical vertebrae 

 participate. The rotatory motion is effected essentially in the articu- 

 lation between the first and second vertebrae ; the latter of which has 

 an arrangement admirably adapting it for this purpose. A toothlike 

 or odontoid process arises from its anterior part, on which the poste- 

 rior surface of the anterior part of the atlas or first vertebra turns as 

 on a pivot. This arrangement has obtained the second vertebra the 

 name vertebra dentata, and its function, that of axis. Rotation to 

 the right is effected by the contraction of the left sterno-mastoid and 

 splenius, and of the right complexus, to the left by the action of the 

 opposite muscles of the same name. The motions of the head aid the 

 senses of sight, hearing, and smell; and are useful in the production 

 of the different vocal tones, by occasioning elongation or decurtation 

 of the trachea and vocal tube. They are, likewise, inservient to ex- 

 pression. 



The spine, as a whole, and each of the vertebrae composing it, are 

 capable of flexion, extension, lateral inclination, and circumduction. 

 These motions occur in the fibro-cartilages between the vertebrae; and 

 they are more easy and extensive, in proportion to the thickness and 

 width of the cartilages. This is one cause why the motions of the 

 cervical and lumbar portions of the vertebral column are freer than 

 those of the dorsal. The inter vertebral substances or fibro-cartilages 

 possess a remarkable degree of elasticity. They yield somewhat, 

 however, to prolonged pressure ; and hence, after long continuance in 

 the erect attitude, our stature may be sensibly curtailed. We can thus 

 understand, that at night we may be shorter than in the morning. 

 Buffon asserts, that the son of one of his most zealous collaborateurs, 

 M. Gueneau de Montbeillard, a young man of tall stature, lost an 

 inch and a half after having danced all night. The loss must be partly 

 ascribed to the condensation of the adipous tissue beneath the foot. 

 During the flexion of the spine, these cartilages are depressed on the 

 side of the flexure, but they rise on the other; and, by their elasticity, 

 are important agents in the restoration of the body to the erect posi- 

 tion. Where they are thickest the greatest extent of motion is per- 



