524 



The Human Sacrum. 



[May 19, 



comitant variation in the nerves ; and (3) a coincident variation in 

 both nervous system and vertebral column. These varying relations 

 of the nervous system to the vertebral column diminish the value of 

 the spinal nerves in the determination of the serial homologies of the 

 vertebral segments. Further information as to the relative frequency 

 of abnormalities in the disposition of the spinal nerves in the limb- 

 plexuses and the relative frequency of the various modes of corre- 

 lation of the spinal nerves and vertebral column is required before 

 adeq late conclusions can be formulated on this point. One can only 

 indi ate the striking fact that all the examples of variation in the 

 arrangement of the spinal nerves in man and anthropoids are examples 

 pointing to an extension backwards of the limb-plexuses, by the 

 entrance into them of post-axially placed nerves. The evidence of 

 the nervous system favours, therefore, the view rather of extension 

 backwards than forwards of the limbs in relation to the vertebral 

 column, as far as present knowledge enables us to judge. 



When all these points are considered together — the cases of libera- 

 tion of the first sacral vertebra, the mode of articulation of the 

 ilium ; the form of the ligamentous surface and the number of bones 

 forming the sacrum ; the correlated variations ; the examples of 

 asymmetry; and the evidence derived from a consideration of the 

 vertebral column in other vertebrates, of the correlation of the 

 nervous system and the vertebral column, and of the development 

 and ossification of the vertebral column in man — the array of facts 

 presented does not afford much support to the theory of a phylo- 

 genetic shortening of the vertebral column advocated by Rosenberg. 

 The conclusion to which these facts lead is rather that there is in 

 the human vertebral column a certain limited variability in the cor- 

 relation of the several parts. The actual variations met with may 

 be in the direction of elongation or abbreviation of a particular 

 region, and more often produce elongation than contraction of the 

 prsesacral region. There is no evidence to show that any definite 

 process of either shortening or lengthening of the vertebral column 

 is going on phylogenetically. The variations found are apparently 

 individual peculiarities ; which, however, taken together, indicate a 

 tendency to elongation rather than contraction of the presacral 

 region. 



At the same time, these investigations give support to the view 

 put forward by Rosenberg and Topinard, that a process of fusion 

 of the rudimentary caudal vertebras with the sacrum is going on, 

 in consequence of the immobility of the caudal appendage, and re- 

 sulting in an increase posteriorly of the number of sacral vertebrae, 

 and a diminution, pari passu, in the number of free caudal vertebrae. 



3. The sacral index was computed in a large number of cases, 

 including 100 Europeans, 20 Andamanese, 9 Negroes, 10 ancient 



