SPINAL CORD. 



301 



Fig. 174* 



and corresponds with the attachment of the nerves which are intended for 

 the supply of the lower limb. 



In form, the spinal cord is a flattened cylinder, and presents on its an- 

 terior surface a fissure, which extends into the cord to the depth of one- 

 third of its diameter. This is the Jissura longitudinalis anterior. If the 

 sides of the fissure be gently separated, they will be seen to be connected 

 at the bottom by a layer of medullary substance, the anterior commissure. 



On the posterior surface another fissure exists, w'hich is so narrow be- 

 tween the second cervical and second lumbar nerve, as to be hardly per- 

 ceptible. This is the Jissura longitudinalis posterior. It extends more 

 deeply into the cord than the anterior fissure, and terminates in the grey 

 sujpstance of the interior. These two fissures divide the medulla spinalis 

 into two lateral cords, which are connected to each other by the white 

 commissure which forms the bottom of the anterior longitudinal fissure, 

 and by a commissure of grey matter situated behind the former. On either 

 side of the fissura longitudinalis posterior is a slight line which bounds on 

 each side the posterior median columns. These columns are most appa- 

 rent at the upper part of the cord, near the fourth ventricle, where they 

 are separated by the point of the calamus scriptorius, and where they form 

 the bulbous enlargement at each side, called processus clavatus. 



Two other lines are observed 

 on the medulla, the anterior 

 and posterior lateral sulci, cor- 

 responding with the attach- 

 ment of the anterior and poste- 

 rior roots of the spinal nerves. 

 The anterior lateral sulcus is a 

 mere trace, marked only by 

 the attachment of the filaments 

 of the anterior roots. The pos- 

 terior lateral sulcus is more 

 evident, and is a narrow grey- 

 ish line derived from the grey 

 substance of the interior. 



Although these fissures and sulci indicate a division of the spinal coi i 

 into three pairs of columns, namely, anterior, lateral, and posterior, the 

 posterior median columns being regarded as a part of the posterior co- 

 lumns, it is customary to consider each half of the spinal cord as consist- 

 ing of two columns only, the antero-lateral and the posterior. The antero- 

 lateral columns are the columns of motion, and comprehend all that part 

 of the cord situated between the fissura longitudinalis anterior and the 

 posterior lateral sulcus, the grey line of origin of the posterior roots of the 

 spinal nerves. The posterior columns are the columns of sensation. 



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

 may be seen and examined. It will 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 grey substance, 



* Sections of the spinal marrow in different portions of its length. 1. Opposite the 

 1th dorsal vertebra. 2. Opposite the 10th dorsal. 3. Opposite the 8th dorsal 4 Op- 

 posite the 5th dorsal. 5. Opposite the 7th cervical. 6. Opposite the 4th cervical. 7. 

 Opposite the 3d cervical. 8. Section of medulla oblongata through the corpora oli 



