i 9 4 HEAD AND NECK 



regarded as a rule, that where a lateral spinal artery gives a branch to 

 one of the postero-lateral arterial trunks, it does not furnish another 

 to the antero-median arterial trunk. In this way different lateral spinal 

 arteries are in connection with the longitudinal trunks on the anterior 

 and posterior aspects of the medulla spinalis. The postero-lateral vessels 

 end at the lower extremity of the medulla spinalis. 



From the five main arterial channels which thus extend along the spinal 

 medulla numerous anastomosing twigs ramify in the pia mater. 



Veins of the Medulla Spinalis. These veins are small and 

 numerous, and their disposition cannot be said to correspond 

 with that of the arteries. They are very tortuous, and form 

 a plexus with elongated meshes. Six more or less perfect 

 longitudinal venous trunks may be noticed on the surface of 

 the medulla spinalis in connection with this plexus ; two of 

 these are median, and are placed respectively on the anterior 

 and posterior aspects. The anterior trunk runs upwards 

 under cover of the antero-median spinal artery. The other 

 four are lateral, and are situated two on either side, in 

 relation, respectively, to the anterior and posterior nerve-roots. 



Upon each side, the veins of the medulla spinalis effect 

 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. 

 Linea splendens. 



POSTERIOR SURFACE. 

 i. The postero-lateral arteries in 



relation to the posterior nerve- 

 2. Single anterior spinal artery in roots 



median plane. 2 Fila of origm of posterior 



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. 



nerve-roots entering themedulla 

 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 

 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. A good deal 

 can be learned by a naked-eye inspection of cross sections of 



