THE VERTEBKAL COLUMN AS A WHOLE. 



101 



vertebrae of the thoracic region, thus causing a slight lateral displacement, together 

 with a flattening of the side of the fifth thoracic vertebra (impressio aortica) as was 

 first pointed out by Wood (Journ. Anat. and Physiol. 

 vol. iii.). Above and below this curve there are slight 

 compensatory curves in the opposite direction. 



The line which unites the tips of the spinous pro- 

 cesses is not a repetition of the curves formed by the 

 bodies. This is due to the fact that the length and 

 direction of the spinous processes vary much in different 

 regions ; thus, in the neck, with the exception of the 

 second, sixth, and seventh, they are all short (absent in 

 the case of the atlas). In the thoracic region the spinous 

 processes, though long, are obliquely placed a circum- 

 stance which much reduces their prominence ; that of 

 the seventh thoracic vertebra is usually the longest 

 and most slanting. Below that point their length 

 gradually decreases, and their position more nearly 

 approaches the horizontal. In the loins the spinous 

 processes have all a slight downward direction. 



The spinous processes of the -upper three or four 

 sacral vertebrae form an osseous ridge with interrupted 

 tubercles. The ridge formed by the vertebral spines 

 is an important determinant of the surface form, as 

 it .corresponds to the median furrow of the back, 

 and there the individual spines may be felt and 

 counted from the seventh cervical down to the sacral 

 region. That is best done when the back is well 

 bent forwards. 



Taken as a whole, the spinous processes of the movable 

 vertebrae in man have a downward inclination a character 

 which he shares with the anthropoid apes and a few other 

 animals. This character serves to distinguish his column from 

 those of lower mammals in which the spines of the lumbar 

 vertebrae are directed head wards towards the "centre of motion," 

 which is usually situated near the caudal extremity of the 

 thorax, where a vertebra is placed the direction of whose 

 spine is vertical to the horizontally disposed column ; this 

 vertebra is often referred to as the anticlinal vertebra. 



As viewed from the front, the vertebral bodies 

 increase in width from the second cervical to the 

 first thoracic; thence a reduction in breadth takes 

 place to the level of the fourth thoracic, below which 

 there is a gradual increase in their transverse dia- 

 meters until the sacrum is reached. There a rapid 

 reduction in width takes place, terminating inferiorly 

 in the nodules of the coccyx. 



The transverse processes of the atlas are wide and 

 outstanding. The succeeding four cervical vertebrae 

 have transverse processes of nearly equal width ; the 

 seventh, however, displays a marked increase in its 

 transverse diameter, and is about equal in width to 

 the first thoracic vertebra. Below this a gradual and 

 regular diminution in width characterises the trans- 

 verse processes of the thoracic vertebrae, until in the 

 case of the eleventh and twelfth they are merely 

 represented by the small lateral tubercles. In the 

 lumbar region the transverse processes again appear outstanding, and of nearly 

 equal length. 



The transverse diameter of the lateral parts of the first sacral vertebra forms 

 the widest part of the column. Below that, a decrease in width occurs until the 



FIG. 115. VERTEBRAL COLUMN 

 FROM THE LEFT SIDE. 



