DEGENERATION OF THE PYRAMIDAL TRACTS. 



709 



have the same result, viz., to produce hemiplegia. (For the subsequent effects, see 

 p. 649.) In a case of congenital absence of the left fore-arm, Edinger found that 

 the right central convolutions were less developed. 



CQ 



Fig. 492, 



Fig. 493. 



Fig. 492. Secondary descending degeneration in middle third of right crus and medulla, after 

 destruction of the cortical motor centres on the right side. Fig. 493. Horizontal section 

 of the cerebral peduncle in secondary degeneration of the pyramidal tracts, where the lesion 

 was limited to the middle third of the posterior segment of the internal capsule. F, healthy 

 crusta ; L, locus niger ; P, internal third of the crusta on the diseased side ; D, secondary 

 degeneration in the middle third of the crusta ; CQ, corpora quadrigemina with the iter 

 below them. 



It is doubtful if the muscular sense is represented in the motor areas ; Nothnagel supposes it 

 to be located in the temporal parietal lobes. It is to be noted, however, that in man there may 

 be general loss of the muscular sense or of motor representations, and, on the other hand, a pure 

 motor paralysis without loss of the former. 



Ataxic motor conditions, similar to those that occur in animals (p. 700), take place in man, 

 and are known as cerebral ataxia. 



The position of the centres is given at p. 696. 



[But we may have localised lesions affecting one or more of the cortical motor 

 areas ; these are called monoplegia. Cases in man are now sufficiently numerous 

 to permit of accurate diagnosis.] Crural monoplegia [rare lesions recorded in the 

 convolutions at the upper end of the fissure of Rolando, and the continuation of 

 this area on to the paracentral lobule of the marginal convolution], brachio- 

 crural, more common, in the upper and middle thirds of the ascending frontal and 

 ascending parietal convolutions brachial, brachio-facial facial, the last in the 

 lowest part of the central convolutions. 



Paralysis of the muscles of the neck and throat indicates a lesion of the central convolutions, 

 and so does paralysis of the muscles of the eye. Lesions of the cortex always cause simultaneous 

 movements of the head and eyeballs. 



Irritation of the Motor Centres. If the motor centres are irritated by patho- 

 logical processes, such as hyperaemia, or inflammation in a syphilitic diathesis 

 more rarely by tumours, tubercle, cysts, cicatrices, fragments of bone there arise 

 spasmodic movements in the corresponding muscle-groups. This condition of a 

 sudden discharge of the grey matter resulting in local spasms is called " Jacksonian, 

 or cerebral epilepsy." 



[Convulsions and spasms may be discharged from motor cortical lesions, and 



