76 THE NERVOUS SYSTEM 



Several longitudinal furrows are seen upon the surface of the cord (Figs. 51, 

 52). Along the middle line of the ventral surface is the deep anterior median 

 fissure (fissura mediana anterior). This extends into the cord to a depth 

 amounting to nearly one-third of its anteroposterior diameter and contains a 

 fold of pia mater. Along the middle line of the dorsal surface there is a shallow 

 groove, the posterior median sulcus (sulcus medianus posterior). As may be 

 seen in cross-sections of the spinal cord, it is divided into approximately sym- 

 metric lateral halves by the two furrows just described and by the posterior 

 median septum (Figs. 55, 56, 57). On either side, corresponding to the line of 

 origin of the ventral roots, is a broad, shallow, almost invisible groove, the 

 anterolateral sulcus (sulcus lateralis anterior). And again on either side, cor- 

 responding to the line of origin of the dorsal roots, is the narrower but deeper 

 posterolateral sulcus (sulcus lateralis posterior). These six furrows extend the 

 entire length of the spinal cord. In the cervical region an additional longi- 

 tudinal groove may be seen on the dorsal surface between the posterior median 

 and posterolateral sulci, but somewhat nearer the former. It is known as the 

 posterior intermediate sulcus and extends into the thoracic cord, where it grad- 

 ually disappears. 



Funiculi. By means of these furrows and the subjacent gray matter each 

 lateral half of the cord is subdivided into columns of longitudinally coursing 

 nerve-fibers known as the anterior, lateral, and posterior funiculi (funiculus 

 anterior, funiculus lateralis et funiculus posterior). In the cervical and upper 

 thoracic regions the posterior intermediate sulcus divides the posterior funiculus 

 into a medial portion, the fasciculus gracilis, and a lateral portion, the fasciculus 

 cuneatus. 



Nerve Roots. From the lateral funiculus in the upper four to six cervical 

 segments there emerge, a little in front of the dorsal roots of the spinal nerves, 

 a series of root filaments which unite to form the spinal root of the accessory 

 nerve (Fig. 125). This small nerve trunk ascends along the side of the cord, 

 enters the cranial cavity through the foramen magnum, and carries to the 

 accessory nerve the fibers for the innervation of the sternocleidomastoid and 

 trapezius muscles. 



From the posterolateral sulcus throughout the entire length of the spinal 

 cord emerge an almost uninterrupted series of root filaments (fila radicularia). 

 Those from a given segment of the cord unite to form the. dorsal root of the cor- 

 responding spinal nerve. The filaments of the ventral roots emerge from the 

 broad, indistinct anterolateral sulcus in groups, several appearing side by side, 



