492 Dr. D. J. Cunningham. 



manner in which the lumbar convexity gives place to the sacral con-; 

 cavity. In the European this takes place in the lumbo-sacral disk of 

 cartilage, and is sharp and sudden, forming a very decided angle. In 

 the Australian it is so gradual and undecided that in the first instance 

 I sketched the lumbar curve so as to include the first sacral vertebra. 

 Such a curve line, however, falls about 1 mm. behind the central point 

 of the lumbo-sacral disk. It is bust therefore to consider that the 

 lumbar curve, as in the European, ends in that disk. But the sacral 

 concavity does not begin at once. If the central points of the lumbo- 

 sacral disk, the first sacral vertebra, and the first sacral disk be joined, 

 it will be found that they lie in a straight line, and that the sacral 

 concavity only begins in the first sacral disk. The close association 

 which is thus established between the first piece of the sacrum and 

 the lumbar column is very largely due to the oblique position which is 

 assumed by the last lumbar vertebra. This is a striking peculiarity, 

 and constitutes perhaps one of the most characteristic features of the 

 Australian spine. In my " Cunningham Memoir " I describe a 

 European spine, in which the first sacral vertebra is actually included 

 in the lumbar curve, but this was brought about in a different 

 manner. It was not due to a shifting of the last lumbar vertebra, 

 but to a shifting of the first sacral element which had separated 

 itself from its neighbours, and thus become associated with the 

 lumbar column. 



A glance at the tracing of the Australian spine is sufficient to show 

 that the lumbar column is constructed upon principles which are 

 calculated to render it exceedingly flexible and elastic. When we 

 look at the corresponding region of the European an impression of 

 great stability is conveyed to the mind. 



In the Chimpanzee, the cervico-dorsal point of inflexion, as in the 

 European, is placed in the disk between the second and third dorsal 

 vertebras. In the spine figured in fig. 1 the dorsal and lumbar axial 

 curves meet in the central point of the twelfth dorsal vertebra, but in 

 the other specimens which I have examined, the point of demarcation 

 between these curves corresponded to the central point of the inter- 

 vertebral disk between the twelfth and thirteenth dorsal vertebrae. 

 The flatter dorsal curve of the Australian therefore involves a greater 

 length of the vertebral column than the corresponding deeper curve 

 in the Chimpanzee and European. 



But, further, the lumbar axial curve in the Chimpanzee involves 

 one or two of the sacral vertebrae. In the spine of the female Chim- 

 panzee figured in the text, the first and second sacral vertebrae are 

 included, but in other specimens examined, only the first sacral 

 element falls into the line of the lumbar curve. An important grada- 

 tion is thus established by the Australian spine, in which the first 

 sacral vertebra has just escaped being included in the axial curve of 



