282 NERVOUS SYSTEM. 



columns, the transmission is mainly through the anterior 

 columns, the lateral columns being much less important. 

 In the cervical region, the conditions are reversed, tad the 

 conduction takes place chiefly by means of the lateral col- 

 umns. Passing from above downward, therefore, the motor 

 fibres are situated in the cervical region mainly in the lateral 

 columns ; but progressively, as they pass through the dorsal 

 and the lumbar portions of the cord, these fibres change 

 their location and are found chiefly in the anterior col- 

 umns. 



llecent observations have not sustained the old idea that 

 the lateral columns of the cord contain fibres which preside 

 specially over the movements of the thorax. The experi- 

 ments of Yulpian upon this point are conclusive. If the 

 lateral column be divided on one side at about the third or 

 fourth cervical vertebra, there is considerable enfeeblement 

 of the muscles of the thorax upon the corresponding side, 

 but there is also partial loss of power in the limbs, which is 

 more marked in the anterior extremity. This diminution 

 in pow r er in the thoracic muscles is such, that in ordinary 

 tranquil respiration, the side corresponding to the section 

 does not move ; but in difficult respiration, or in crying, the 

 movements are very marked. 



Decussation of the Motor Conductors of the Cord. Well- 

 established anatomical and pathological facts show conclu- 

 sively that there is a complete decussation of the motor con- 

 ductors of the cord ; so that the stimulus of volition gen- 

 erated in one lateral half of the brain always passes to the 

 opposite half of the body. If a lesion occur in the brain 

 upon one side, so as to produce total paralysis of motion, the 

 opposite side of the body is paralyzed, while voluntary mo- 

 tion is absolutely intact on the side corresponding to the 

 injury. In the anterior pyramids of the medulla oblongata, 



1 VULPIAN, Systeme nerveux, Paris, 1866, p. 371. 



