318 



ANATOMY OF 



which decussate ; the two halves of the cerebrum, the cerebellum 

 and spinal chord, being united by commissures. MM. Magendie 

 and Desmoulins, just as Prochaska, Barthez, Sabatier, Boyer, 

 Dumas, Bichat, and Chaussier did before them, deny the decus- 

 sation ; but it was known of old, as Gall remarks in his demon- 

 stration of it, and cannot be disputed. The following, from Mr. 



a, Corpora olivaria; b, Corpora pyra- 

 midalia, seen to discussate at their low- 

 est part, where are three sets of ascend- 

 ing fibres on each half one turning 

 from behind c, the corpora restiformia, 

 another running straight, and the third 

 decussating. This writer, however, 

 speaks of them not as ascending, but 

 descending. 



Mayo, shows it well. This forms an exception to the rule ob- 

 served in every other part of the cranial nervous organs, except 

 the optic nerves and the fibres which run from the genitals to 

 the cerebellum, of the nervous fibres, destined to each side of 

 the body, running on the same side of the brain ; and we hence 

 explain why injuries of one side of the brain, causing paralysis, 

 generally influence the opposite side of the body. d The spinal 

 chord has no decussation, whence injuries of one side of it in- 

 fluence the corresponding half of the body. Decussation has not 

 been discovered in the cerebellum ; and vivisectors say that an 

 injury of a cerebellic hemisphere affects the same side ; but Gall 

 found that extirpation of a testicle caused the opposite lobe of 

 the cerebellum to shrink. 6 



After their decussation, the bands of the anterior corpora py- 

 ramidalia ascend on the ANTERIOR part of the chorda oblongata 

 (called by Gall the grand reriflement), enlarging as they proceed. 

 As soon as they enter among the transverse fibres of the meso- 

 cephalon, called by Gall the great commissure of the cerebellum, 

 they divide into many bundles, which are imbedded in a large 

 quantity of pulpy substance, from which proceed many fibres, 



d I have never known an exception to this ; but exceptions are recorded, and 

 probably some difference of situation is the reason of the difference of effect. 



e 1. c. vol. iii. p. 112. sqq. Sur les Fonctions du Cerveau, t. iii. p. 291. sqq. 

 Dr. Vimont has repeated Gall's experiments with the same results. Traitc de 

 Phrtnologie humaine et c&mparee, par J. Vimont, M. D. 2 vols. 4to. with an 

 atlas of 120 plates. Paris, 18325. vol. ii. p. 233. 



