THE SPINAL CORD. 



circumference, by the posterior lateral sulcus (Fig. 101). The 

 sulcus is situated opposite the posterior columna of gray matter, 

 to which it transmits the posterior roots of the spinal nerves. It 

 is continuous above with the posterior lateral sulcus of the medulla. 

 It separates the posterior surface and the antero-lateral surface 

 from each other. 



Anterior Root-line. (S. lateralis anterior). As a landmark, 

 it is convenient to call the longitudinal line through which issue 

 the most lateral fibers of the anterior roots of the spinal nerves, 

 the anterior root-line of the spinal cord (Fig. 101). There is no 

 groove on the surface of the cord along this line and it is misleading 

 to call it a sulcus, as has been the custom. It is situated opposite 

 the anterior columna of gray matter and in line with the anterior- 

 lateral groove of the medulla oblongata. Through it and through 

 the surface, just medial to it, emerge the anterior roots of the 

 spinal nerves. It subdivides the antero-lateral surface into ante- 

 rior and lateral surfaces. 



The posterior intermediate sulcus (s. intermedius posterior) 

 is a slight longitudinal groove in the cord which subdivides the 

 upper three-fourths of the posterior surface into postero-medial 

 surface and postero-lateral surface (Fig. 101). From it a con- 

 nective tissue septum extends into the cord and separates the fas- 

 ciculus gracilis and fasciculus cuneatus from each other. The 

 posterior intermediate furrow is found only in the cervical and 

 in the upper eight thoracic segments of the cord. 



i. GRAY MATTER OF THE CORD. 



The spinal cord is composed of (i) gray matter (substantia 

 grisea spinalis), in the central part; and (2) white matter (sub- 

 stantia alba spinalis) in the peripheral area. It is like the medulla 

 and pons in having the white matter on the surface (Fig. 101). 



A column of gray matter (Fig. 101), crescentic in section, 

 extends through the center of each lateral half of the spinal cord. 

 The crescent is convex medially; and is joined to its fellow, a 

 little in front of the middle, by a vertical transverse lamina of 

 gray matter, called the gray commissure (commissura grisea). 



