IS 



VERTEBRAL COLUMN. 



Fig 15. 



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II' T 





Fig. 15. — Vertebral Column op an Adult Male, 



SEEN FROM BEHIND (A. T.). ^ 



C 1 to above D 1, the seven cervical vertebroe ; 

 D 1 to above L 1, the t-\velve dorsal vertebroe ; L 1 

 to above iS 1, the five lumbar vertebras ; S 1 to above 

 CO 1, the sacrum ; CO 1, aud below, the four coccy- 

 geal vertebra;. The transition in the form of the trans- 

 verse processes and tubercles is well marked in this 

 specimen. 



The vertebral column as a whole. — 



The vertebral column may be regarded as a 

 central column upon which the other ])arts 

 of the skeleton are arranged. Superiorly it 

 supports the skull, laterally the ribs, through 

 which also it receives the weight of the 

 upper limbs, and near its lower extremity it 

 rests upon the pelvic bones, by which it 

 transmits the weight of the body to the lower 

 .limbs. It is a pillar of support to the rest of 

 the skeleton, and protects the spinal cord 

 by enclosing it in a bony canal. Its average 

 length is about 28 inches. 



When seen in profile the column presents 

 four curves, directed alternately forwards 

 and backwards, — forwards in the cervical 

 and lumbar regions, backwards in the dor- 

 sal and sacral. The cervical and lumbar 

 convexities are produced by the greater 

 thickness of the anterior over the posterior 

 parts of the intervertebral discs, and in the 

 case of the latter also by the greater depth 

 of the fifth lumbar body anteriorly, while in 

 the dorsal and sacral concavities, tlie bodies 

 of the vertebrce are thinner in front than 

 behind. These curves are connected with 

 the maintenance of the erect posture, and 

 give to the column greater elasticity and 

 security from injury than it would have 

 were it perfectly straight. In the dorsal 

 region also there is very frequently a slight 

 degree of lateral curvature, the convexity of 

 which, in most cases, is directed towards 

 the right side, and is probably connected 

 with the greater use made of the right than 

 of the left arm. 



Viewed in front, the bodies of the vertebree 

 are seen to become broader from the axis 

 to the first dorsal, then slightly narrower 

 to the fourth dorsal, and from that ver- 

 tebra they gradually widen to the base of 

 the sacrum. The width between the ex- 

 tremities of the transverse processes is con- 

 siderable in the atlas ; small in the axis, it 



