THE SPINAL CORD 



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This functional differentiation of the neural axis into sensor and motor divisions apparently 

 finds organic expression in an important modification of the developing neural tube. Each 

 lateral wall of the neural tube is early demarcated into a dorsal and a ventral strip or lamina 

 and the slit-like central canal becomes more or less lozenge-shaped on trans-section, owing to 

 the formation of a lateral longitudinal furrow within. The dorsal lamina or zone is preponder- 

 atingly sensor in function, while the ventral zone is principally motor in function. This funda- 

 mental fact has been of the greatest aid in the correct interpretation of many hitherto obscure 

 facts regarding the mechanism of the nerve system, and will be found to underlie our method of 

 description throughout. 



The muscular supply from motor segments of the cord is shown in Fig. 604, 

 and the cutaneous supply in Fig. 605. 



Internal Structure of the Spinal Cord. If a transverse section of the spinal 

 cord be made, it will be seen to consist of white and gray nerve substance. The 

 white substance is made up of myelinated axones; the gray contains the cell 

 bodies of neurones and nonmyelinated axones. The color of the gray substance, 

 so-called, varies according to the degree of capillary injection and the age of the 

 individual. It is usually of a faint, reddish-gray tinge, the gray preponderating in 

 older persons, but various shades of red, yellow, and light-slate color may be noted. 



DORSAL GROOVE 



DORSAL SEPTUM 



DORSAL ROOT 



DORSO-LATERAL 

 FISSURE 



RETICULAH 

 FORMATION 



LATERAL HORN 



VENTRAL HORN 



SO O"* S VENTRAL FISSURE 



FIG. 606. Trans-section of the spinal cord at the mid-thoracic region. 



Xor is the color uniform even in the same section. Around the central canal and 

 at the periphery of the dorsal horn the gray substance is very translucent and 

 is termed, according to its situation, the gelatinosa centralis (gliosa centralis) 

 and gelatinosa- Rolandi or caput gliosum (gliosa cornualis). The white substance 

 surrounds the gray column as a variously thickened tunic, closely invested by the 

 pia, which sends numerous delicate, vessel-bearing ingrowths into the substance of 

 the cord. The relative area of the white substance, as seen on section, increases 

 cephalad ; the absolute area of both white and gray is the largest in the region of 

 the enlargements (Fig. 607). 



Gray Substance of the Cord (eniocinerea; subsiantia grisea centralis}. A plastic 

 conception of the gray substance of the cord is essential to an understanding of 

 the internal architecture. The gray core must be imagined not alone in the 

 relations in which it is conventionally studied, as exposed in trans-sections, but 



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