222 



The Spinal Cord 



That part of the anterior column which is to the outer side of 

 Tiirck's column consists of fibres destined for the anterior roots of the 

 spinal nerves ; its strands, therefore, are for motor conduction. 



In the lateral column are two strands of fibres, one of which passes 

 to the cerebellum, the direct cerebellar tract, the other being the crossed 

 pyramidal tract. The latter is composed of fibres which have crossed 

 in the decussation of the anterior pyramids of the medulla oblongata 

 (those fibres of the pyramid which have not so decussated passing down 

 in Tiirck's column). Thus, secondary to disease of the motor area of 

 the cerebrum say of the right side degeneration occurs in the right 

 direct (Tiirck's) tract and in the left crossed tract. 



(The direct cerebellar tract is for the transmission of sensory im- 

 pulses, as indicated in the diagram on p. 215.) 



Disease of the antero-lateral column causes loss of voluntary action 

 "of the muscles below, and, control from the brain being lost, the re- 

 flexes are exaggerated and a spasmodic contraction results teta?ioid 

 paraplegia. But the muscles implicated are not wasted unless the 

 sclerosis extends into the anterior cornu, and 

 there is no loss of sensation or of co-ordina- 

 tion, for the posterior columns are still sound. 

 Children are specially subject to sclerosis of the 

 lateral column, the disease being generally called 

 spastic paraplegia. The child gradually loses 

 the power of walking, and as he is being exa- 

 mined a storm of reflexes may arise * his knees 

 are thrown up in bed and his thighs are violently 

 adducted. When he tries to walk a character- 

 istic spasm of the muscles of locomotion prevents 

 him, his heels being drawn up and his limbs 

 stiffened. All the reflexes are in excess, and that 

 -* of the ankle is so strong that rhythmic contrac- 

 muscles t ions are replaced by muscular rigidity. (The 

 reflex loops are entire, but the cerebral control 

 cannot travel down to them by the diseased motor paths.) Subse- 

 quently the muscles become contractured, the hands and feet are 

 * clawed,' and the patient is hopelessly bed-ridden. 



As already remarked, the motor area of the brain is held in com- 

 munication with the anterior roots of the spinal nerves by means of the 

 pyramidal tracts chiefly the crossed tract with the intervention of 

 the large multipolar cells of the anterior cornu. And thus, if a muscle of 

 the arm, for instance, be paralysed, the fault may be in the motor area 

 of the brain, in a pyramidal tract, in the ganglionic cells, or in the 

 efferent filaments of the nerve. 



Descending degeneration. In the case of a lesion of the motor 

 area of the brain (p. 48) say of the right side degeneration descends 

 by the pyramidal tracts, those muscles being paralysed on the left side 



