STRUCTURE OF THE GREY SUBSTANCE OF THE SPINAL CORD. 361 



The posterior cornua are divisible into two portions sharply 

 separated from each other, an anterior (fig. 221, c) and a 

 posterior, which last, owing to its peculiar translucency when 

 examined with the naked eye, has long been known as the 

 substantia gelatinosa of Rolando (fig. 221, d). This part of 

 the grey substance is the poorest in nervous elements, and is 

 distinguished from other parts essentially by the circumstance 

 that it does not contain the fine nerve-fibre plexus ; on the 

 other hand, it contains a large amount of connective tissue, 

 which, however, presents certain peculiarities ; for, of the three 

 morphological constituents of the connective tissue, the finely 

 granular matrix, the cellular elements, and the fine fibrils that 

 I regard as elastic, the last-mentioned is present in extra- 

 ordinarily small quantity, whilst the cellular elements are very 

 abundant in the form of nuclei surrounded with a variable 

 quantity of protoplasm. This affords an explanation of the 

 circumstance that, in good carmine-tinted specimens, the sub- 

 stantia gelatinosa, next to the epithelium of the central canal, 

 is the most deeply stained tissue. The nervous elements of the 

 substantia gelatinosa are limited to small horizontally running 

 fasciculi of nerve fibres which partly proceed from the posterior 

 roots, and in part from the posterior columns ; they however 

 only traverse the gelatinous substance, pursuing a straight 

 course through its centre, but laterally being more or less 

 arched, and anteriorly entering that portion of the posterior 

 cornua which possesses a nerve-fibre plexus (fig. 221, d). As 

 regards, finally, the form of the substantia gelatinosa, when seen 

 in transverse section it is an elongated oval in the cervical and 

 dorsal regions, whilst in the lumbar it is more circular. It 

 adjoins the posterior columns internally and rather posteriorly, 

 as well as the posterior roots of the nerves ; externally and in 

 part also posteriorly it is invested by a thin lamina of the grey 

 substance of the posterior horns, that possesses a nerve-fibre 

 plexus, in which sometimes even larger nerve cells occur, and 

 immediately anterior to which are the vertical fasciculi of the 

 grey substance (fig. 221, h, and fig. 229, d). 



The anterior division of the posterior cornua is extra- 

 ordinarily rich in fibres running partly horizontally, partly 

 vertically; the former characterized by their repeated divi- 



