WHITE SUBSTANCE OF TELENCEPHALON 



885 



radiate to the cortex of the pre- and post-central gyri, the sensory-motor or somsesthetic area 

 of the hemisphere. The majority terminate in the post-central gyrus. 



All the fibres connecting the cerebral cortex with both the thalamus and the hypothalamic 

 nucleus belong to the so-called projection fibres of the cerebral hemisphere. 



The habenular nucleus and the fasciculus retroflexus of j\le\Tiert have been noted in the de- 

 scription of the rhinencephalon. The habenular nucleus, a part of the epithalanaus, is a small 

 group of nerve cells situated in the habenular trigone just infero-lateral to the epiphysis. The 

 fibres of the medullary stria of the thalamus (habenula) terminate about its cells. A small 

 bundle of fibres crossing the mid-line under the epiphysis in the superior aspect of the posterior 

 cerebral commissure is called the commissure of the habemdce, from the fact that it connects the 

 habenular nuclei of the two sides. 



Fig. 697. — Oblique Frontal Section through the Brain in the Direction of the 

 Cerebral Peduncles and the Pyramids. (Seen from in front.) (After Toldt, "Atlas 

 of Human Anatomy," Rebman, London and New York.) 



Longitudinal fissure 

 Radiation of corpus callosum 



Septum pellucidum 



Superior frontal gyrus 



Body of corpus caUosum 



Chorioid plexus of lat- 

 eral ventricle 



Corona radiata 



Column of fornix - 



Chorioid plexus of [ -• 

 third ventricle ^l"^----^ 



Internal capsule 



Thalamus 

 Third ventricle —j 



Interpeduncular —Li 

 fossa 



Inferior cornu of 

 lateral ventricle 



Cerebral peduncle 



Brachium ponti 



Longitudinal pyrami 

 fasciculi of pons 



Anterior horn of lateral ventricle 

 Head of caudate nucleus 



Radiation of corpus 

 striatum 



Cerebellum 



Superficial fibres of pons / 

 Pyramid 



/ Putamen 



,< External capsule 



^ Insula 



- Claustrum 



Globus pallidus 

 '~'-~ Optic tract 



Mammillary body 

 Oculo-motor nerve 



Trigeminal nerve 



Facial and cochlear 

 nerves 



Flocculus 



Glosso-pharyngeal nerve 

 Vagus nerve 



Inferior olivary nucleus 

 Decussation of pyramids 



The fasciculus retroflexus (Meynerti) is a relativelj^ strong bundle of meduUated fibres 

 which runs downward and then turns caudalward from the habenular nucleus toward the inferior 

 portion of the interpeduncular fossa. It has been shown that many, at least, of the fibres of 

 this bundle arise from the cells of the habenular nucleus. In its slightly caudad course, the 

 bundle passes obhquely through the red nucleus, entering the medial superior aspect and making 

 its exit from the ventro-mesial side of the inferior extremity of this nucleus. In the animals in 

 which it has been studied, the bundle ends in the inter-peduncular nucleus (ganglion), a group of 

 nerve cells lying in the floor of the interpeduncular fossa at the level of the inferior quadrigemina. 

 In man, the interpeduncular nucleus is not definitely assembled and the bundle seems to dis- 

 appear in the posterior perforated substance. However, the microscope shows cells dispersed 

 among the fibres of the bundle and these cells probably represent the nucleus. 



The white substance of the telencephalon. — A horizontal section through the 

 upper part of the trunk of the corpus callosum will pass above the basal grey 

 substance of the corpus striatum, and, aided by the corpus callosum, each hemi- 

 sphere in such a section wall appear as if consisting of a solid, half-oval mass of 

 white substance, bounded without by the grey layer of the cortex (fig. 672) . As 



