Vertebral Column 13 



toiamen nor facet, but are distinguished by the massive size of their bodies and arches 

 and the thickness and square cut of their spines. In the figure (Fig. 9) these differ- 

 ences are exemplified by drawings of vertebrae from the middle of their respective 

 regions. At the same time it is seen that a costal element must be considered as entering 

 into the composition of most of the vertebrae. This forms a free rib in the dorsal 

 series, but is included in the so-called transverse process in the other regions, and in 

 the sacrum. In the cervical series the costal element forms the front wall of the 

 vertcbr -arterial foramen, so that the " transverse process " really is a compound of a 

 true transverse element and a costal element, separated by the foramen and joined by 

 a coslo-transverse bar. In the dorsal region the transverse process is a true one, and 

 not compound, but in the lumbar region it is really a costal process, the true transverse 

 element being reduced and its tip represented by the small accessory process that is 

 visible behind the base of the costal element. 



In the sacrum the different morphological constituents of the bone can also be 

 recognised, as will be pointed out at a later stage. 



Before examining the special characters of the individual vertebras the articulated 

 column should be considered as a whole. The discs account for more than one-fifth of the 

 total length of the column. A striking character of the complete column is the presence 

 of curves : there are four of these in the sagittal plane, convex forward in the cervical 

 and lumbar regions, concave forward in the dorsal and sacral. The dorsal curve is 

 primary, and can be looked on as the persisting curve of the embryonic axis. The 

 sacral curve is referred to as primary also. The other two curves are secondary and 

 compensatory, the cervical bend appearing towards the end of foetal life to enable the 

 head to be raised from the thorax, while the lumbar curve results from the assumption 

 of the upright sitting posture and extension of the legs, therefore appearing after 

 birth. The sharp bend between the lumbar and sacral regions is a modification in the 

 general curve that begins to appear in the second half of intrauterine life. 



The primary curves have corresponding differences between the front and back 

 heights of the bodies of their respective vertebras : in the acquired and compensatory 

 curves the bend is accounted for mainly by corresponding differences in height in the 

 intervertebral discs. This is specially marked in the lumbar convexity, where the 

 curve is altogether -due to the ventral thickness of the discs in lower races : in higher 

 races the sum of the front measurements of the bones is higher than that of the posterior 

 surface of the bodies, so that the curve is not altogether due to the discs. The lumbo- 

 sacral disc is about two and a half times as thick in front as behind. 



The greater depth of the fronts of the lumbar bodies in Europeans is really confined 

 to the lower two or three members of the series. In lower races the bodies, except the 

 last, are shallower in front. 



The curves of the -column become more accentuated up to puberty, and the dorsal 

 curve appears to increase somewhat in length and depth after general growth has 

 ceased. 



The most anterior part of the cervical convexity is the front of the body of the fourth cervical 

 vertebra, and the curve ends below about the second dorsal : the body of the seventh or eighth 

 dorsal usually forms the point of greatest posterior projection in the dorsal curve, which ends 

 usually below the first lumbar vertebra. 



Compare male and female columns, and observe that the sacrum in the woman 

 is turned back to a greater extent. This would make a more prominent lumbo-sacral 

 angle, but it is modified by the lumbar curve becoming more pronounced : thus in 

 women the fourth lumbar is usually more prominent forward than in men. 



The presence of curves in the column above the sacrum adds to its elasticity. 



