86 OSTEOLOGY. 
Not infrequently there is a slight lateral curvature in the dorsal region, the 
convexity of the curve being usually directed towards the right side. This may be 
associated with a greater use of the muscles of the right 
upper limb, or may depend on the pressure exercised “by 
the upper part of the thoracic aorta on the vertebre of the 
dorsal region, thus causing a shght lateral displacement. 
Above and below this curve there are slight compensatory 
curves in the opposite direction. 
The lne which unites the tips of the spines is not a 
repetition of the curves formed by the bodies. This is due 
to the fact that the length and direction of the spines vary 
much in different regions; thus in the neck, with the ex- 
ception of the second, sixth, and seventh, the spines are all 
short (absent in the case of the atlas). In the thoracic region 
the spines, though long, are obliquely placed—a circumstance 
which much reduces their prominence; that of the seventh 
thoracic vertebra is usually the longest and most slanting. 
Below this point the length of the spies gradually decreases, 
and their position more nearly approaches the horizontal. 
In the loins, the spines have all a shght downward direction. 
‘ 
Cervical 
Taken as a whole, the spines of the movable vertebree 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 vertebrze are directed headwards towards the 
“centre of motion,’ which is usually situated near the hinder ex- 
tremity of the thorax, where a vertebra is placed the direction of 
whose spine is vertical; this vertebra is often referred to as the 
anticlinal vertebra. 
Thoracie 12 
The spines of the upper three or four sacral vertebree 
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 here the individual spines may be felt and 
counted from the seventh cervical down to the sacral region. 
This is best done when the back is well bent forwards. 
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 diameters until the sacrum is reached. 
Here a rapid reduction in width takes place, terminating 
inferiorly in the nodules of the coccyx. 
The transverse processes of the atlas are wide and out- 
standing. 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 transverse processes of the thoracic 
vertebre, until in the case of the eleventh and twelfth they 
are merely represented by the small external tubercles. In 
the lumbar region the transverse processes again appear 
Fic. 66.—VERTERRAL Coruuy OUtstanding, and of nearly equal length. 
AS SEEN FROM BEHIND. The transverse diameter of the lateral mass of the first 
sacral vertebra forms the widest part of the column. Below 
this a decrease in width occurs until the level of the third sacral segment is reached, 
at which point the transverse diameter is somewhat abruptly diminished, a reduction 
in width which is further suddenly accentuated opposite the fifth sacral segment. 
Lumbar 5 
Sacral 5 
Cocey- 
geal 4-5 
