72 
THE VOYAGE OF H.M.S. CHALLENGED. 
working quite independently of each other, and on two distinct series of skeletons of 
various races of men, it is obvious that differences exist amongst them in the relative 
thickness of the bodies of the lumbar vertebrae anteriorly and posteriorly. The produc- 
tion of bone in the bodies of the lumbar vertebrae of these races has been so adjusted 
that they are collectively thicker in front than behind in the white races, and behind 
than in front in the black races. If the spinal column consisted only of the osseous 
vertebrae in direct articulation with each other, both by their articular processes and 
bodies, the lumbar region would then be concave forward in the black races, and convex 
forward in the white races. But the spine, in addition to the osseous vertebras, contains 
an intercalated series of intervertebral elastic discs, and these discs may perhaps be 
so adjusted in the black races as to be collectively thicker in front than behind in the 
lumbar region, and thus to compensate for the want of development in depth of 
the anterior surface of the vertebral bodies, and to give to the column a forward 
convexity in that region as in the white races, although not perhaps in so well-marked a 
degree. Should this be the case, it would follow that in the course of the development and 
ossification of the spinal column in the lumbar region in these races, important differences 
would arise anteriorly and posteriorly in the proportion of that mesoblast tissue which 
becomes cartilage and bone, and that which becomes intervertebral disc. We have no in- 
formation, however, on the thickness of the discs in the black races, either relatively or 
absolutely, so that this interesting question is not in a position to be definitely answered. 
Putting on one side, therefore, for the present, the question of modifications in the 
relative thickness of the discs, and limiting ourselves to the consideration of the 
influence which the bodies of the vertebrae themselves would have on the curvature of 
the spine, we find a very considerable range of variation in the vertical diameter 
anteriorly and posteriorly of the series of five lumbar vertebrae. These diff"erences are 
expressed numerically by the . general lumbar index. In my series of skeletons the 
lowest index was in a Chinese, 8 4 '8, and the highest both in a Bushman and in a male 
Hindoo, 106, but Dr. Cunningham has obtained, as the mean of tw^o male Tasmanians, 
an index as high as 108*5, and of ten male Australians, 110"1. Without at present 
taking into consideration the compensatory arrangements in the living body which 
might modify these relative diff"erences in thickness, the lumbar spine — so far as repre- 
sented by the bodies of its vertebrae, and with the lower surface of the body of one 
vertebra in contact with the upper surface of the body of the vertebra next below — might 
present one or other of three forms in difi"erent races of men. It might be convex 
forwards, or straight, or concave forwards, and to each group an arbitrary numerical 
limit might be assigned, based on the general lumbar index. We might assume that 
such a series of vertebrae, with the general lumbar index calculated only from the vertical 
diameters of the lumbar bodies, and ranging from 98 to 102, both inclusive, formed a 
straight spine, Orthorachic {opdos, straight, /5ax^^' spine) ; one with a general index 
