STRUCTURE OF THE GREY SUBSTANCE OF THE SPINAL CORD. 359 



facilitated by admitting the existence of an intermediate por- 

 tion, situated behind the anterior comu and in front of the 

 posterior cornu of each side. The anterior cornua are cha- 

 racterized by the presence of groups of large cells, of which 

 three or more may be distinguished in the cervical and lumbar 

 portions of the spinal cord which are more or less distinctly 

 defined. The largest of these cell groups, which at the same 

 time extends farthest backwards, is the lateral (fig. 217, ?i), 

 the smallest is the median (fig. 217, 'p) t whilst the third (fig. 

 217, o) is a trifle larger than this last, and is situated externally 

 and in front of the lateral one. These groups coalesce to a 

 greater or less extent in the anterior cornua of the thoracic 

 region, where the number of nerve cells is considerably smaller. 

 In the anterior cornua isolated nerve cells of variable size also 

 occur, which do not belong to any particular cell group. These 

 cornua are moreover traversed by broad, partly isolated, partly 

 fasciculated nerve fibres, which, either as aiding to form the 

 anterior roots, unite with the nerve processes of the cells, or as 

 fibres originating in the nerve-fibre plexus, enter the anterior 

 columns of the opposite or the lateral columns of the same 

 half of the spinal cord. The semi-fibrous plexus is every- 

 where supported by connective tissue, except in the immediate 

 vicinity of the nerve cells, which consequently, both in gold 

 and carmine-tinted preparations that have been washed and 

 preserved in Canada balsam, are always surrounded by a tole- 

 rably clear area, which may fairly be ascribed to the presence 

 of unstained and therefore transparent connective tissue. 



The middle part of the two lateral halves of the spinal column 

 only contains, in the dorsal region, isolated groups of cells. 

 These are the columns of Lockhart Clarke, to which allusion 

 has already so frequently been made, and which are situated 

 laterally to, and somewhat behind, the grey commissure. These 

 groups are most strongly developed in the middle of the dorsal 

 portion of the cord ; i.e., they here contain the largest number 

 of medium-sized nerve cells. Towards the cervical as well as 

 the lumbar regions of the cord they progressively diminish in 

 number, and at the commencement of the cervical and lumbar 

 enlargements altogether disappear. In gold-tinted preparations 

 I have discovered sharply defined fasciculi of fibres closely 



