HISTOLOGY OF THE CENTRAL NERVOUS SYSTEM OF THE WEDDELL SEAL, 853 
cells is situated; the cells of Clarke’s column are also seen, having been 
displaced below the base of the posterior horn by mechanical pressure. 
(c) A broad anterior horn possessing several groups of large nerve-cells. 
The white matter in the posterior region shows but slight indication of a division 
into postero-mesial and postero-lateral columns: the lateral columns are of relatively 
wide extent. 
Fic. 2.—A transverse section of the spinal cord (mid-dorsal region). Lettering as in fig. 1, except :-— 
a.m. Arachnoid mater. | m. Posterior roots. 
c.c. Central canal of cord. a.s.v. Anterior spinal vessels, 
The posterior nerve-roots are narrower than in the cervical region, but are very 
well defined : the root-bundles lie just outside, and are seen cut across in the section. 
The anterior roots pass out in three or four narrow strands. 
The proportion of grey matter to white is as 9 to 20 approx. 
Compared with higher types, the dorsal cord shows but few divergences: the 
posterior horn of grey matter is rather shorter than in the human cord, and Clarke’s 
column of nerve-cells is but feebly developed. On the other hand, the motor cells in 
the anterior horn are very well defined. 
