268 NORMAL HISTOLOGY. 



the lateral between the dorsal and ventral root-lines, and the anterior between 

 the ventral root-line and median fissure. The conventional division between 

 the anterior and lateral columns, however, is largely artificial, since neither 

 superficially nor internally is there a definite demarcation between these 

 tracts. In the lower cervical and upper thoracic cord, the posterior column 

 is subdivided by the superficial paramedian sulcus and a septum of neuroglia 

 into two wedge-shaped tracts, of which the median and smaller is the fascic- 

 ulus gracilis or tract of Goll and the lateral and larger is the fasciculus 

 cuneatus or tract of Burdock. 



The Gray Matter. Within each half of the cord the gray matter 

 forms a comet-shaped area, the broader end of which lies in front and the 

 narrow one behind, with the concavity directed laterally. The convex 

 mesial surfaces of the areas of the two sides are connected by a transverse 

 band of gray matter, the gray commissure, that extends across the mid- 

 line and encloses the minute central canal of the cord. The connecting 

 band is subdivided by the canal into the posterior and the anterior gray 

 commissure, which lie behind and in front of the tube respectively. The 

 posterior median septum reaches the dorsal surface of the gray commissure, 

 but the ventral margin of the latter is separated from the bottom of the 

 anterior median fissure by an intervening bridge of white matter, the anterior 

 white commissure, which connects the anterior columns and provides an 

 important pathway for fibres passing from one side of the cord to the other. 



Each crescent of gray matter is divided conventionally into three 

 parts: the anterior and posterior cornua, the ventral and dorsal extremities 

 of the crescent that project beyond the line of the transverse gray commis- 

 sure, and the pars intermedia, that connects the cornua and receives the 

 commissure. The two horns differ markedly and, although varying in 

 details at different levels, retain their distinctive features throughout the 

 cord. The anterior cornu, or columna grisea anterior, is short thick and 

 rounded and separated from the surface by a considerable layer of white 

 matter, through which the ventral root-fibres pass to their points of emerg- 

 ence from the cord. The blunt tip of the anterior horn is known as the 

 capui cornu and the dorsal portion, by which it joins the commissure and 

 the pars intermedia, as the basis cornu. The posterior cornu, or columna 

 grisea posterior, is relatively long narrow and pointed and extends almost to 

 the postero-lateral sulcus. The tip or apex of the dorsal horn is formed of a 

 A-shaped stratum, the subslantia gelatinosa Rolandi, that appears lighter 

 and somewhat less opaque than the subjacent caput cornu, which it covers as 

 a cap. The slightly contracted ventral portion of the posterior horn is the 

 cervix cornu. 



The fairly sharp demarcation between the gray and white matter is 

 interrupted along the lateral border of the crescent by prolongations of gray 

 matter into the adjacent lateral column (Fig. 322). The subdivisions oi 

 these processes unite into a reticulum of gray matter, the meshes of which 

 are occupied by longitudinally coursing nerve-fibres, the whole interlacement 

 being known as the formatio reticularis. This structure is best developed in 

 the upper cervical region, where it is a conspicuous network filling the recess 

 between the pars intermedia and the neck of the posterior cornu. In the 

 thoracic region, the formatio reticularis is condensed into a compact lateral 

 projection of gray matter, the lateral cornu, or columna lateralis. 



The histological components of the gray matter include the nerve- 

 ceils, the nerve-fibres and the supporting neuroglia. Of these the most 

 distinctive elements are the multipolar nerve-cells, which lie embedded 



