.64 Anatomy OF the Nervous System 



across the median plane in the rodents, but in man is distinctly 

 paired. 



The close association of the oculomotor and trochlear 

 nuclei with the medial longitudinal bundle is a significant 

 example of neurobiotaxis (p. 49), this tract containing the 

 majority of the fibres which carry stimuli to their cells. 



Various correlation nuclei also occur in the tegmentum, 

 among which, two important centres are the dorsal and ventral 

 tegmental nuclei {nucleus tegmenti dorsalis or nucleus ventralis 

 grisea centralis, and nucleus tegmenti ventralis or nucleus of 

 V. Gudden). These occur at the extreme posterior end of the 

 midbrain and are better developed in the rodents than in 

 man (PI. XII.). The dorsal nucleus lies immediately dorsal 

 to the medial longitudinal bundle, a little behind the troch- 

 lear nucleus. Between the levels of Pis. XI and XII it 

 appears as a large rounded mass rather clearly outlined by a 

 diffuse capsule of fine fibres. It receives fibres from the 

 interpeduncular nucleus through the tegmental tract of that 

 centre and from the mamillary body through the mamillo- 

 tegmental tract {tractus mamillo-tegmentalis, tract of v. Gudden) . 

 Its axons descend in a system of scattered longitudinal fibres 

 close to the ventricular surface {dorsal longitudinal bundle 

 of Schtitz, periependymal longitudinal tract), which extends 

 back from the thalamic region but is most distinct at and 

 behind the level of this nucleus. The ventral nucleus is a 

 conspicuous mass ventral to the medial longitudinal bundle, 

 in which also many mamillo-tegmental fibres end. These 

 nuclei are apparently relay-stations on a reflex pathway 

 from the hypothalamus to the motor nuclei of the hindbrain. 

 The mamillo-tegmental tract is difficult to distinguish in 

 the lower part of its course in transverse sections prepared by 

 Weigert's method. It is a group of fine fibres which curve 

 backward in the vertical plane after leaving the mamillary 

 body, and run dorso-posteriorly through the tegmentum on 

 each side of the raphe, to end in the nuclei just described. 



