8 



THE SPINAL CORD. 



The concave side of each lateral crescent faces outward, and in consequence of the 

 depth of the posterior median fissure the commissure of grey matter joins the crescents 

 nearer their anterior than their posterior ends, except in the lumbar region of the cord. 

 The two horns or cornua of each crescent are named from their position anterior 

 and posterior (or, better, ventral and dorsal) ; the anterior or ventral horn (fig. 8, 

 a. c) is the shorter and broader, and is everywhere separated from the surface of the 

 cord by white matter which is traversed by the bundles of the anterior roots at the 

 part where these enter the cord. The posterior or dorsal horn (p. c} is longer and 

 narrower, and tapers almost to a point (apex cornu posterioris), which closely 



Fig. 8. SECTION OF THE SPINAL CORD IN THE UPPER PART OF 



THE DORSAL REGION. (E. A. S. ) \ 



a, anterior median fissure ; p, posterior-median fissure ; p, n, 

 posterior nerve-roots entering at the postero- lateral groove ; a, c, 

 anterior cornu of grey matter ; p, c, posterior cornu ; i, inter- 

 medio-lateral tract (lateral cornu) ; p, r, processus reticularis ; c, 

 posterior vesicular column of Clarke ; , pia-matral septum form- 

 ing the lateral boundary of the postero-mesial column. 



approaches the external surface of the cord at the 

 postero-lateral groove, with which it is connected 



by a process of the superficial neuroglia which here dips in towards the horn, 

 but is interrupted by a stratum of fine nerve-fibres known as the marginal 

 bundle. The posterior horn is slightly narrowed at its base (cervix cornu} ; from 

 that place it gradually expands into the main part of the horn (caput cornu), and 

 from this it tapers in the way just noticed. Near its tip the caput cornu has a 

 peculiar semi-transparent aspect, an appearance due to the siibsiantia gelatinosa of 

 Eolando (fig. 14), which forms a kind of cap to the cornu. The part of the grey 

 crescent between the two horns is known as the intermediate grey substance (Gowers). 



Near the middle of the outer surface of each crescent the grey matter is less 

 sharply marked off than elsewhere from the white matter ; portions of grey matter 

 extending into the lateral white column and uniting with one another into what in 

 sections appear like a network enclosing portions of white substance (p. r.). This is 

 known as the processus reticularis ; it is best marked in the cervical region (fig. 14). 

 At the postero-lateral part of the anterior horn, immediately in front of the 

 processus reticularis, the grey matter forms in the upper dorsal (thoracic) region 

 (fig. 11, Dl) a somewhat pointed triangular projection, which is sometimes distin- 

 guished as the lateral horn but is better known as the intermedio-lateral tract of 

 Lockhart Clarke (intermediate process of Gowers) (fig. 8, i). Above, in the cervical 

 region, this blends with and forms part of the enlarged anterior horn. This is 

 also the case in the lumbar enlargement, but in the sacral region the lateral horn 

 again becomes distinct. 



The grey crescents vary in form in different parts of the cord (see fig. 9). In 

 the dorsal (thoracic) region both anterior and posterior cornua are narrow. In the 

 cervical and lumbar regions the anterior cornua are large and broad. The posterior 

 cornua are narrow in the cervical and thoracic, but very broad in the lumbar region. 

 The grey matter is seen in a series of sections to be most abundant in the lumbar 

 region of the cord, and least in the thoracic. 



It is clear that what appear in section as irregular crescentic areas of grey matter 

 are in reality long irregularly fluted columns, and that the commissural band uniting 

 the convex edge of the crescents is a flattened expansion, connecting the columns 

 along their whole length. But it is both customary and convenient to speak of the 

 various parts of the grey matter of the cord according to their appearance in sections, 

 although the term " columns" is very generally applied to what appear in section 



