124 



Ib.v 



THE STRUCTURE OF MAN 



thoracic and lumbar portions of the column. 



h. This shortening, as above said, is more 

 apparent than real, for the vertebral column 

 [growing the more rapidly] extends farther 



i> and farther back beyond the posterior 

 limit- of the spinal cord. [It is worthy of 

 remark that this inequality of growth, so 

 marked in Man, is still more conspicuous 

 among certain lower Mammals e.g. the 

 Hedgehog, in which the filum terminale 

 commences in the anterior thoracic region.] 

 The filum terminale (f.t., Fig. 76) 

 runs through the lumbar and sacral 

 regions of the vertebral column into the 

 caudal ; and this terminal filament, which 

 grows with the growing vertebral column, 

 is the vestigial homologue of the posterior 

 portion of a spinal cord which, in the 

 ancestors of Man, may have run evenly 

 throughout the whole length of the 

 vertebral column, as it now does in many 

 lower Vertebrates. This process of reduc- 

 tion, which sets in at the posterior end of 

 the spinal cord, is profoundly significant, 

 as we have already had to describe a 

 similar process of reduction going on at 

 the posterior end of the axial skeleton itself 

 (ante, pp. 28 et seq.}. 



I should like to suggest the consideration 

 whether certain pathological conditions may not 

 be traced to this source, if only indirectly ? I 

 refer to those frequent diseases of the spinal cord 

 known as tabetic, which in by far the greater 

 number of cases arise at its posterior end. May 

 not the above described condition of the lumbar 



FIG 76. LOWER PORTION OF THE SPINAL CORD, WITH THE CAUDA EQUINA AND THE 

 ENVELOPING DURA MATER. (Dorsal aspect.) One -half natural size. (After 

 Schwalbe.) 



The dura matral sheath has been opened up from behind and laid back ; on the left side 

 the roots of the nerves are represented entire ; on the right, the lower of these are 

 shown removed above their passage through the sheath, and the bones of the coccyx 

 are delineated in their natural relative positions, in order to show the relations of the 

 filum terminale and the coccygeal nerves. 



cc., coccygeal nerves ; /.., dorsal longitudinal fissure ; f.t., filum terminale, slightly dis- 

 placed to the right side ; Ib. i and v, first and fifth lumbar nerves ; l.d., ligamentum 

 denticulatum ; sc. i and v, first and fifth sacral nerves ; sh., the dura matral sheath ; 

 th. x and xii, tenth and twelfth thoracic nerves. 



