1434 ^ MANUAL OF ANATOMY 



column of the spinal cord, and are connected with the cells of the 

 ventral cornu of grey matter. 



The superior cerebellar peduncle is almost entirely an ascending 

 tract, but a few of its fibres are regarded as arising within the optic 

 thalamus and as descending to the cerebellar hemisphere. 



Dorsal or Posterior Longitudinal Bundle. — ^This bundle occupies 

 the dorsal part of the tegmentum, and is intimately related to the 

 grey matter which forms the ventral wall or floor of the aqueduct 

 of Sylvius. It lies close to the median raphe, as dofes its fellow of 

 the opposite side, and across the raphe an interchange of fibres 

 takes place between the two bundles. In the spinal cord it is 

 represented by the anterior ground-bundle and the anterior mar- 

 ginal bundle of Lowenthal. In the medulla oblongata it traverses 

 the dorsal part of the pyramid, being separated fiom the pyramidal 

 (motor) fibres by the mesial fillet or chief sensory tract. There- 

 after it traverses the formatio reticularis of the dorsal part of the 

 pons Varolii, and is continued upwards as one of the tracts of the 

 .tegmentum of the cms cerebri. 



The fibres of the dorsal longitudinal bundle are regarded as being 

 the axons of cells belonging to (i) the nucleus of Deiters, which is 

 one of the terminal nuclei of the vestibular root of the auditory 

 nerve, (2) the formatio reticularis of the medulla oblongata and 

 pons Varolii, (3) the formatio reticularis of the tegmentum, (4) the 

 sensory nucleus of the fifth cranial nerve, and (5) the nucleus of the 

 dorsal longitudinal bundle. Inferiorly the fibres of the bundle 

 ramify within the anterior column of the spinal cord in connection 

 with the motor cells of the ventral cornu of grey matter. Superiorly 

 its fibres are intimately related to the following important nuclei — 

 namely, (i) the oculo-motor nucleus, or nucleus of the third cranial 

 nerve; (2) the trochlear nucleus, or nucleus of the fourth cranial 

 nerve; and (3) the abducent nucleus, or nucleus of the sixth cranial 

 nerve, these being the nuclei which control the muscles of the 

 eyeball and upper eyelid. The bundle furnishes numerous col- 

 laterals to each of these nuclei, which terminate in arborizations 

 around their cells. The bundle also establishes connections with 

 the motor nuclei in the pons Varolii and medulla oblongata. 



The dorsal longitudinal bundle extends as high as a special 

 nucleus, called the nucleus of the dorsal longitudinal bundle, which 

 is situated in the grey matter of the ventro-lateral portion of the 

 third ventricle, near the upper opening of the aqueduct of Sylvius, 

 from the cells of which nucleus some of its fibres arise. 



The dorsal longitudinal bundle consists of ascending and descend- 

 ing association-fibres, which form connections between the impor- 

 tant nuclei just referred to. Probably the chief use of the bundle 

 is to maintain a functional association between these nuclei, and 

 insure harmonious action of the muscles which are supplied by the 

 nerves arising from them. 



Ventral or Anterior Longitudinal Bundle. — ^This bundle consti- 

 tutes the tectospinal tract, and it lies on the ventral aspect of the 



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