BASAL GANGLIA OF THE CEREBEAL HEMISPHERE. 



639 



external and internal medullary laminae, are now evident, which traverse its sub- 

 stance in a vertical direction and divide it into three masses. The lateral, basal, 

 and larger mass is termed the putamen ; the two medial portions together constitute 

 the globus pallidus. 



The putamen forms much the largest part of the lentiform nucleus. It is 

 darker in colour than the globus pallidus, and in this respect resembles the caudate 

 nucleus. It is traversed by fine radiating bundles of fibres, which enter it from the 

 external medul- 

 lary lamina. 

 Both in point of 

 structure and in 

 mode of develop- 

 ment it is closely 

 associated with 

 the caudate nuc- 

 leus, and it is the 

 only part of the corpus caiiosum 

 lentiform nucleus 

 which is con- 

 nected by inter- 

 vening bands of 

 gray matter with 

 the caudate nuc- 

 leus. Theantero- 



pOSteriOr length, Septum pellucidum 



as well as the 

 vertical depth of 

 the putamen, is 



Caudate nucleus 



much greater Internal capsule 



than in the Case Nucleus lentiformis 



Claustrum 



Longitudinal 

 fissure 



Lateral ventricle 

 Column of fornix 

 Chorioid plexu 



Foramen inter- 

 ventriculare 



of the globus 



pallidus ; conse- 



quently, in both 



frontal and hori- 



zontal sections 



through the cerebrum it is encountered before the plane of the globus pallidus is 



reached. 



FIG. 568. FRONTAL SECTION THROUGH THE CEREBRAL HEMISPHERES so as to cut 

 through the anterior part (putamen) of the lentiform nucleus in front of the 

 globus pallidus. Viewed from in front ; looking through the anterior horn into 

 the central part of the ventricle. 



The external capsule is loosely connected with the lateral surface of the putamen, and it can be 

 readily stripped off. This accounts for the tendency, exhibited in haemorrhages in this locality, 

 for the effused blood to spread out in the interval between these structures. 



The globus pallidus is composed of the two smaller and medial masses of the 

 lentiform nucleus. They present a faint yellowish tint, and are paler and more 

 abundantly traversed by fibres than the putamen. The mass next the putamen 

 (i.e. the intermediate part) is much larger than the medial subdivision. It extends 

 forwards to a point a little in front of the plane of the anterior commissure. When 

 the lentiform nucleus is cut in a frontal direction, and in its widest part, the 

 medial mass shows an indication of a separation into two parts, so that 'here the 

 globus pallidus appears to consist of three subdivisions. 



Connexions of the Corpus Striatum. Recent clinical investigation has demon- 

 strated the importance of the functions of the corpus striatum, which seems to exercise a 

 "steadying influence" (Kinnier Wilson) upon the muscles which perform voluntary 

 movements that call for delicate co-ordination. Hence it is desirable to study the 

 connexions of these large masses of gray matter. Fibres of the internal capsule coming 

 from the motor cortex (as well as from all other cortical areas) end in the corpus striatum 

 (Fig. 571), so that when a voluntary movement is initiated this structure is called into 

 activity. Fibres coming from the nucleus caudatus break through the anterior limb of 

 the internal capsule (Fig. 572), some of them to reach the putamen, others to pass 

 through the external medullary lamina to the globus pallidus. Other tracts pass from 



