ROOTS OF THE SPINAL NERVES. 363 



rior, efferent or motor root and a posterior, afferent or sensory root 

 (Figs. 100 and 104). These roots descend more or less from their 

 4 cord attachment to the inter- vertebral foramen in which they 

 unite to form the spinal nerve. The roots of the first cervical 

 nerve are horizontal; those of the first thoracic nerve descend the 

 width of two vertebrae, and those of the twelfth thoracic, the width 

 of four vertebrae; while the roots of the coccygeal nerve extend 

 from the first lumbar vertebra to the second piece of the coccyx, 

 through ten vertebrae. 



Anterior Root. In all spinal nerves, except the first, the 

 anterior root (radix anterior} is smaller than the posterior. It is 

 composed of from four to six fasciculi, which soon combine into 

 two bundles. After piercing the dura mater, the anterior root 

 unites with the posterior, beyond the latter' s ganglion, and forms 

 a spinal nerve. The anterior root is efferent, or motor, in func- 

 tion. 



Apparent Origin (Fig. 104). The anterior root is composed 

 of medullated axones which issue from the narrow longitudinal 

 area at the junction of the anterior one-fourth with the posterior 

 three-fourths of the cord's surface. This area is bounded later- 

 ally by the anterior root-line, commonly called the anterior lateral 

 sulcus. 



Real Origin (Fig. 104). These medullated axones rise from 

 the medial, lateral, and intermedio-lateral columns of cell-bodies 

 on the same side of the cord and from the medial column of the 

 opposite side. These cell-bodies of the anterior columnae and 

 the intermedio-lateral column constitute the genetic nuclei (nuclei 

 origines) of the spinal nerves. The fibers of large caliber in the 

 anterior roots rise from the cell-bodies in the anterior columnae. 

 They are voluntary motor fibers. In the intermedio-lateral column, 

 the small fibers of the anterior roots take their origin. They are 

 probably sympathetic in junction, that is, involuntary motor, 

 vaso -motor, viscero-motor, inhibitory, secretory, trophic, inhibito- 

 secretory, and inhibito-trophic. 



Lesions. The lower motor neurones (spinal and cerebral) 

 are probably in a state of toxic irritation in laryngismus stridulus, 

 tetanus, acute ascending paralysis (Landry), strychnine poisoning, 



