92 HEAD AND NECK 



communications with the veins in the vertebral canal by means 

 of small twigs which run laterally on the nerve-roots. 



How to distinguish the anterior from the posterior surface of 

 the medulla spinalis. 



ANTERIOR SURFACE. POSTERIOR SURFACE. 



I. Linea splendens. i. The postero - lateral arteries, in 



relation to the posterior nerve- 

 roots. 



Fila of origin of posterior 

 nerve-roots entering the medulla 

 spinalis along a straight and 

 continuous line, and at the 

 bottom of a distinct sulcus. 



Posterior nerve-roots, larger than 

 the anterior, and provided with 



2. Single anterior spinal artery, in 



median plane. 



3. Anterior nerve - roots, smaller 



than posterior, and springing 

 by fila which emerge from 

 the medulla spinalis, not in a 

 continuous straight line, but 

 irregularly over an area of some 

 width. ganglia. 



Preservation of the Medulla Spinalis. If the medulla spinalis is in a 

 fit state for preservation, it should be immersed for a few weeks in 

 methylated spirit, to which a small amount (4 per cent. ) of formalin has been 

 added. When sufficiently firm, the dissector should endeavour to learn 

 something of its internal structure by making transverse sections across 

 it at different levels, and inspecting the cut surface closely with the naked 

 eye, or with the aid of a magnifying glass. 



Internal Structure of the Medulla Spinalis. The medulla 

 spinalis is composed of an inside core of grey matter which is 

 surrounded on all sides by an external coating of white matter, 

 and a good deal can be learned by a naked-eye inspection of 

 cross sections through it made in different regions and at 

 different levels. 



In such sections the antero-median fissure and the postero- 

 median septum and sulcus, which partially divide it along the 

 whole of its length into right and left halves, become obvious. 



The antero-median fissure is much shorter than the postero- 

 median septum. It dips dorsally to a commissure of white 

 matter, the anterior white commissure, which connects the white 

 matter of the two halves of the medulla spinalis ; and it con- 

 tains a fold of pia mater and branches of the anterior spinal 

 vessels. The postero-median sulcus is a shallow furrow which 

 runs along the posterior surface of the medulla spinalis in 

 the median plane, and the postero-median septum extends 

 from the bottom of the sulcus to a transverse grey com- 

 missure called the posterior commissure, which connects the 

 two halves of grey matter. 



