650 



THE BRAIN STRUCTURE OF THE CEREBRUM. 



corpus striatum (projecting into the lateral ventricles), which in reality is composed of two 

 parts, the nucleus caudatus and lenticular nucleus (fig. 460, b), the optic thalamus which lies 

 behind the former, and bounds the 3rd ventricle (fig. 460, d), the corpora quadrigemina lying on 

 the upper surface of the crura cerebri (fig. 480, hi) ; within the tegmentum of the crura cerebri 

 are the red nucleus and locus niger (fig. 502). Lastly, there is the continuation of the grey 

 matter of* the cord up through the medulla, pons, and around the iter, forming the central 

 grey tube and terminating anteriorly at the tuber cinereum. These various parts are connected 

 in a variety of ways with each other, some by transverse fibres stretching between the two sides 



of the brain, while other longi- 

 tudinal fibres bring the hinder 

 and lower parts into relation with 

 the fore parts.] 



[Under cover of the occipital 

 lobes, but connected with the 

 cerebrum in front, and the spinal 

 cord below, is the cerebeUum, 

 which has its grey matter ex- 

 ternally and its white core inter- 

 nally. Thus we have to consider 

 cereoro-spinal and cerebellospinal 

 connections.] 



Meynert's Projection Systems. 

 The cortex of the cerebrum 

 consists of convolutions and sulci, 

 the "peripheral grey matter" 

 (fig. 461, C), which is recognised 

 as a nervous structure, from the 

 presence in it of numerous gan- 

 glionic cells ( 358, 1). From it 

 proceed all the motor fibres which 

 ure excited by the will, and to it 

 proceed all the fibres coming from 

 the organs of special sense and 

 sensory organs, which give rise to 

 the psychical perception of ex- 

 ternal impressions. [In fig. 461 

 the decussation of the sensory 

 fibres is represented as occurring 

 near the medulla oblongata. It 

 is more probable that a large 

 Fig. 460. number of the sensory fibres de- 



Dissection of the brain from above showing the lateral, 3rd, l^^^^^S^, 

 and 4th ventricles with the basa ganglia and surrounding 463> ^ me obge era assert g 

 parts, a knee of the corpus callosum ;>, anterior part ot some of the sensory fibres decussate 

 the right _ corpus striatum.; b , grey matter dissected oft to in ^ medulla ob J lon ata>] 

 show white fibres; c, points to taenia semicirculans ; d, Firat Projection System. -The 

 optic thalamus ; e, anterior pillars of fornix with 5th ven- channels le J ad to and from the 



tricle in front of them, between the two laminae of the 



3rd 



, cortex cerebri, some of them tra- 

 septum lucidum ; /, middle or soft commissure; g, 3rd yersi th ^ u& 



ventricle; At, corpora quadrigemina; k, superior cere- Ha fa C erebrum-the corpus 



bel ar peduncle ; Z, hippocampus .major ;m, posterior .cornu * fcriatum (a , } (composed of ? he 



of ; lateral ventncle; 71, eminentia collaterahs; 4th ven- caudate ^ an A d lent icular 



tncle ; p, medulla oblongata ; s, cerebellum, with r, arbor nudeus (N ^ optic thalamu8 



(T.o), and corpora quadrigemina 

 some fibres form connections with cells within this central grey matter. The fibres which 

 proceed from the cortex through the corona radiata in a radiate direction constitute Meynert's 

 first projection system. Besides these, the white substance also contains two other systems of 

 fibres : (a) Commissural fibres, such as the corpus callosum and the anterior commissure (c, c), 

 which are supposed to connect the two hemispheres with each other ; and (b) a connecting or 

 association system, whereby two .different areas of the same side are connected together (a, a). 

 The ganglionic grey matter of the basal ganglia forms the first stage in the course of a large 

 number of the fibres. "When they enter the central grey matter, they are interrupted in their 

 course. According to Meynert, the corona radiata contains bundles of fibres from the corpus 

 striatum (1, 1), lenticular nucleus (2, 2), optic thalamus (3, 3), and corpora quadrigemina (4, 4). 

 The second projection system consists of longitudinal bundles of fibres, which proceed down- 

 wards and reach the so-called " central grey tube," which is the ganglionic grey matter reaching 



