COLUMNS OP THE SPINAL CORD. 385 



filaments of the anterior roots. The posterior lateral sulcus is more 

 evident, and is formed by a narrow grayish fasciculus derived from 

 the gray substance of the interior. 



These sulci divide the medulla into four fasciculi or cords, viz. 



Anterior columns, 

 Lateral columns, 

 Posterior columns, 

 Median posterior columns. 



The Anterior are the motor columns, and give origin to the motor 

 roots of the spinal nerves. They are continued upwards into the 

 medulla oblongata, under the form of corpora pyramidalia. 



The Lateral columns are divided in their function between motion 

 and sensation, and contain the fasciculus described by Sir Charles 

 Bell as the respiratory tract. Some anatomists consider the ante- 

 rior and lateral column on each side as a single column, under the 

 name of antero-lateral. 



The Posterior are the columns of sensation, and give origin to the 

 sensitive roots of the spinal 'nerves. Their superior terminations are 

 named corpora restiformia. 



The Median posterior columns have no function at present assigned 

 to them. 



If a transverse section of the spinal cord be made, its internal 

 structure may be seen and examined. It would then appear to be 

 composed of two hollow cylinders of white matter, placed side by 

 side, and connected by a narrow white commissure. Each cylinder 

 is filled with gray substance, which is connected by a commissure 

 of the same matter. The form of the gray substance, as observed 

 in the section, is that of two half moons placed back to back, and 

 joined by a transverse band. The horns of the moons correspond 

 to the sulci of origin of the anterior and posterior roots of the nerves. 

 The anterior horns do not quite reach this surface ; but the posterior 

 appear upon the surface, and form a narrow gray line. 



The white substance of the spinal cord is composed of parallel 

 fibres which are collected into longitudinal lamina; and extend 

 throughout the entire length of the cord. These laminae are various 

 in breadth, and are arranged in a radiated manner ; one border being 

 thick and corresponding with the surface of the cord, while the other 

 is thin and lies in contact with the gray substance of the interior. 

 According to Rolando the white substance constitutes a simple 

 nervous membrane which is folded into longitudinal plaits, having 

 the radiated disposition above described. The anterior commissure 

 according to his description is merely the continuation of this ner- 

 vous membrane from one lateral cord across the middle line to the 

 other. Moreover, Rolando considers that a thin lamina of pia mater 

 is received between each of the folds from the exterior, while a layer 

 of the gray substance is prolonged between them from within. 

 Cruveilhier is of opinion that each lamella is completely independent 

 of its neighbours, and he believes this statement to be confirmed by 



49 



