NERVE 



195 



6th. In the spinal cord they constitute the crossed 

 pyramidal tract of the opposite side. Those which do not 

 cross run down for some distance in the antero-median 

 tract as the direct pyramidal fibres to cross lower down 

 (fig- 98). 



7 th. From the pyramidal fibres collaterals come off 

 and act, through intercalated neurons, on the outgoing 

 neurons from the anterior horn of 

 grey matter to the skeletal muscles 

 (fig. 33). These pyramidal fibres de- 

 generate when the motor cortex is 

 destroyed or when they are severed by 

 a haemorrhage into the internal 

 capsule. 



Fibres from the Basal Ganglia. — De- 

 generation of the rubro-spinal and of the 

 tecto-spinal fibres does not occur unless 

 this interruption is below the level 

 of the tectum (p. 1 1 3). 



The course of the various outefoingf 

 fibres in the spinal cord in man is 

 shown in fig. 98, 



In addition to the tracts from the 

 cerebrum, the downgoing fibres forming Fig. 97.— To show the 

 the outgoing part of the vestibulo- grfro^^Kfex 

 cerebello - spinal arc are also shown of the Precentral Con- 



(fig. 98). volution. 



— tkr*it^fi^iniid»l Tr^^ 



IV. Outgoing Nerves from the Spinal Cord. 



These outgoing nerves from the spinal cord emerge in 

 the anterior roots (p. 107). They may be divided into two 

 sets : — 



1. Somatic, to the skeletal muscles. 



2, Visceral, to the viscera, blood-vessels, glands, etc. 



1. Somatic. — The course and distribution of these are 

 fully studied in anatomy. 



2. Visceral. — These outgoing fibres are characterised by 

 their small size. They take origin, as described on p. .54, 

 chiefly in a lateral column of cells, which is well developed 



