606 THE SPINAL COED. 



the sacral canal, or to the base of the coccyx. Internally, it is a prolongation 

 for about half its length of some of the nervous elements of the cord ; 

 externally, it consists of a tube of the pia mater or innermost membrane, 

 which, being attached at its lower end to the dura mater and vertebral 

 canal, keeps pace with the latter in its growth, whilst the cord relatively 

 shortens. It is distinguished by its silvery hue from the nerves amid which 

 it lies. Small blood-vessels may sometimes be seen upon it. 



Fissures. When removed from the vertebral canal, and divested of its 

 membranes, the spinal cord is seen to be marked by longitudinal fissures. 

 Of these, two, which are the most obvious, run along the middle line, 

 one in front and the other behind, and are named the anterior and pos- 

 terior median fissures. 



The anterior median fissure is more distinct than the posterior, and pene- 

 trates about one-third of the thickness of the cord, its depth increasing 

 towards the lower end. It contains a fold or lamelliform process of the pia 

 mater, and also many blood-vessels, which are thus conducted to the centre 

 of the cord. At the bottom of this fissure is seen the transverse connecting 

 portion of white substance named the anterior white commissure. 



The posterior median fissure is less marked in the greater part of its 

 extent than the anterior, but becomes more evident towards the upper part 

 of the cord. In a certain sense it is no real fissure, except at the lumbar 

 enlargement and in the cervical region, in both of which places a superficial 

 fissure is distinctly visible ; for, although the lateral halves of the posterior 

 part of the cord are quite separate, there is no distinct reflection of the pia 

 mater between them, but rather a septum of connective tissue and blood- 

 vessels which passes in nearly to the centre of the cord, as far as the posterior 

 grey commissure. 



Besides these two median fissures, two lateral furrows or fissures have 

 been described on each side of the cord, corresponding with the lines of 

 attachment of the anterior and posterior roots of the spinal nerves. 



The posterior lateral fissure is a superficial depression along the line of 

 attachment of the posterior roots, and is at the edge of the plane in which 

 these roots pass inwards to the grey matter of the cord. 



The anterior lateral fissure, which is often described in the line of the 

 origin of the anterior roots of the nerves, has no real existence as a groove. 

 The fibres of these roots in fact, unlike the posterior, do not dip into the 

 spinal cord in one narrow line, but spread over a space of some breadth. 

 The grey substance of the cord, however, approaches the surface somewhat 

 in the vicinity of the place where the anterior roots enter : and this, together 

 with a slight depression, produces the appearance which has been described 

 as a groove. Thus, each lateral half of the cord is divided by the posterior 

 lateral fissure into a posterior and an antero-lateral column ; and although 

 we cannot trace an anterior lateral fissure, this antero-lateral portion of the 

 cord may, for the convenience of description, be considered as subdivided 

 into an anterior and a lateral column by the internal grey matter. 



On the posterior surface of the cord, and most evidently in the upper 

 part, there are two slightly marked longitudinal furrows situated one on 

 each side, close to the posterior median fissure, and marking off, at least in 

 the cervical region, a slender tract, named the posterior median column.. 

 Between the anterior and posterior roots of the spinal nerves, on each side, 

 the cord is convex, and sometimes presents a longitudinal mark correspond- 

 ing with the line of attachment of the ligamentum denticulatum. 



Foville states, that in a new-born child there is a narrow accessory bundle of white 



