(Fig. 672) . The portion of the medulla spinalis which lies in front of the postero- 

 lateral sulcus is termed the antero-lateral region. The anterior nerve roots, unlike 

 the posterior, are not attached in linear series, and their position of exit is not 

 marked by a sulcus. They arise by separate bundles which spring from the anterior 

 column of gray substance and, passing forward through the white substance, 

 emerge over an area of some slight width. The most lateral of these bundles is 

 generally taken as a dividing line which separates the antero-lateral region into 

 two parts, viz., an anterior funiculus, between the anterior median fissure and the 

 most lateral of the anterior nerve roots; and a lateral funiculus, between the exit 

 of these roots and the postero-lateral sulcus. In the upper part of the cervical 

 region a series of nerve roots passes outward through the lateral funiculus of the 

 medulla spinalis; these unite to form the spinal portion of the accessory nerve, 

 which runs upward and enters the cranial cavity through the foramen magnum. 



Entire secHon. 



i ii in \v. v vi MI MII i ii in iv v 



vn viu ix \ xi XH i n m iv\- 1 uiuuvJ 





FIG. 665. Curves showing the sectional area at different levels of the cord. The ordinates show the area in sq. mm. 



(Donaldson and Davis.) 









The Internal Structure of the Medulla Spinalis. On examining a transverse 

 section of the medulla spinalis (Fig. 664) it is seen to consist of gray and white 

 nervous substance, the former being enclosed within the latter. 



Gray Substance (substantia grisea centralis). The gray substance consists of 

 two symmetrical portions, one in each half of the medulla spinalis: these are 

 joined across the middle line by a transverse commissure of gray substance, through 

 which runs a minute canal, the central canal, just visible to the naked eye. In a 

 transverse section each half of the gray substance is shaped like a comma or 

 crescent, the concavity of which is directed laterally; and these, together with 

 the intervening gray commissure, present the appearance of the letter H. An 

 imaginary coronal plane through the central canal serves to divide each crescent 

 into an anterior or ventral, and a posterior or dorsal column. 



The Anterior Column (columna anterior; anterior cornu), directed forward, is 

 broad and of a rounded or quadrangular shape. Its posterior part is termed the 

 base, and its anterior part the head, but these are not differentiated from each other 

 by any well-defined constriction. It is separated from the surface of the medulla 

 spinalis by a layer of white substance which is traversed by the bundles of the 

 anterior nerve roots. In the thoracic region, the postero-lateral part of the anterior 

 column projects lateralward as a triangular field, which is named the lateral column 

 (columna lateralis; lateral cornu). 



The Posterior Column (columna posterior; posterior cornu) is long and slender, 

 and is directed backward and lateralward: it reaches almost as far as the 'postero- 

 lateral sulcus, from which it is separated by a thin layer of white substance, the 

 tract of Lissauer. It consists of a base, directly continuous with the base of the 

 anterior horn, and a neck or slightly constricted portion, which is succeeded by 

 an oval or fusiform area, termed the head, of which the apex approaches the postero- 

 lateral sulcus. The apex is capped by a V-shaped or crescentic mass of trans- 

 lucent, gelatinous neuroglia, termed the substantia gelatinosa of Rolando, which 



48 



