1414 A MANUAL OF ANATOMY 



the nucleus of the facial nerve; others pass to the nucleus of the 

 hypoglossal nerve; but the majority of them are destined for the 

 motor cells in the anterior grey cornu of the spinal cord. The 

 fibres which pass to the facial nucleus lie close to the genu, and 

 those which pass to the hypoglossal nucleus lie close behind the 

 facial fibres. The fibres of the pyramidal tract occupy the central 

 portion of the crusta of the cms cerebri in their downward course. 



The postlenticular part of the posterior limb contains the following 

 sets of fibres : (i) the fibres of the optic radiation, on their way 

 from and to the optic thalamus, external geniculate body, and 

 superior quadrigeminal body ; (2) the fibres of the auditory radia- 

 tion, passing between the auditory region of the temporal lobe and 

 the internal geniculate body ; and (3) ' the fibres of the temporo- 

 pontine tract (cortico-protuberantial fibres), which pass from the 

 cortex of the temporal lobe through the outer part of the crusta 

 of the cms cerebri to the pons Varolii, where they terminate 

 in the nucleus pontis. The internal capsule is continuous inferiorly 

 with the crusta of the cms cerebri. Superiorly its fibres diverge 

 in a radiating manner on their way to the cerebral cortex, forming 

 the corona radiata, the fibres of which are intersected by those of 

 the radiatio corporis caUosi. 



The external capsule is a thin lamina of white matter which is 

 situated on the outer side of the nucleus lenticularis, where it lies 

 between that nucleus and the claustmm. In front of and behind 

 the nucleus lenticularis it is continuous with the internal capsule. 

 The external capsule is, as stated, only loosely connected with the 

 putamen of the nucleus lenticularis. The fibres of which it is 

 composed are probably derived from the anterior white commissure 

 and the optic thalamus. 



Connections of the Corpus Striatum. — (i) The nucleus caudatusand nucleus 

 lenticularis are partly continuous with each other, and partly connected by 

 striae of grey matter. (2) The corpus striatum is connected with the optic 

 thalamus by strio-thalamic and thalamo-striate fibres. (3) The nucleus 

 caudatus is said to be connected with the substantia nigra by a tract of fibres 

 known as the stratum intermedium. (4) The nucleus lenticularis is connected 

 with the optic thalamus by the ansa lenticularis. (5) The corpus striatum is 

 connected with the cerebral cortex by cortico-striate fibres. 



Development. — The corpus striatum is developed as a thickening of the 

 floor of the cerebral vesicle. 



The claustrum is a thin lamina of grey matter which is situated 

 on the outer surface of the external capsule. It lies embedded in 

 the white matter which occupies the region between the lenticular 

 nucleus and the island of Reil. Superiorly it is narrow and tapering, 

 but inferiorly it expand^ and reaches the surface at the base of the 

 brain, in the region of the locus perforatus anticus. Its outer 

 surface presents elevations and intervening depressions, which 

 correspond to the sulci and gyri of the island of Reil. 



The claustrum is regarded as an isolated portion of the grey 

 matter of the island of Reil. 



The amygdaloid nucleus is an oval collection of grey matter 

 which is situated in the anterior part of the temporal lobe, where 



