306 



NORMAL HISTOLOGY. 



intermingled with many nerve-fibres. The cells of the globus pallidus, save 

 for their somewhat smaller size (2040^) and a lighter pigmentation, re- 

 semble the smaller neurones of the caudate nucleus, but are less generally 

 cells of type II. Large neurones (35-70 /*) are common in the putamen, 

 having a slender cell-body and giving off at the poles two or more dendrites. 

 The axone often arises from the base of a dendritic process. 



The Thalamus. This large ovoid ganglionic mass lies between the 

 third ventricle mesially, of which cavity it constitutes the lateral wall, and 

 the internal capsule laterally. Its free dorsal surface, and to a less degree 

 the mesial as well, is covered with a thin layer of nerve-fibres, the stratum 

 zonale, whilst ventro-laterally the thalamus is separated from the internal 

 capsule by a denser layer of fibres, the external medullary lamina. The 

 gray matter is subdivided into two general parts, the lateral and the mesial 

 nucleus, by a vertical sheet of white matter, the internal medullary lamina. 

 The periphery of the lateral nucleus is broken up by numerous fibres passing 



Medullary branch 



Larger pial artery 



White matter 



Pia within fissure - 

 FIG. 352. Injected cerebral cortex, showing capillary supply of gray and white substance. X 18. 



from the thalamus into the internal capsule into a reticular zone, sometimes 

 called the latticed layer. The nerve-cells of the thalamic nuclei include three 

 chief varieties: (i) the stellate cells (35-50 /*), distinguished by their richly 

 branched dendrites that radiate in all directions; (2) the brush-cells, so called 

 on account of the brush-like expansions of their dendrites, spindle or trian- 

 gular and from 20-40 n in diameter; and (3) the polygonal cells, few but 

 large (50-60 /*), with a number of long slender tortuous dendrites. The 

 thalamic cells are by no means uniformly distributed, but, on the contrary, 

 are aggregated into larger and smaller groups, the subsidiary nuclei; of 

 these eleven are distinguished by Cajal, by whom they are described as 

 lying in three general planes and constituting a lateral, an intermediate and 

 an inner series. Of these the ventro- lateral nucleus is of especial impor- 

 tance, since it probably receives the afferent fibres of the great sensory fillet- 

 tract. In a general way, the neurones of the thalamus may be regarded as 

 receptors of a large part of the afferent impulses carried to the cerebrum 

 from the cerebellum, brain-stem and spinal cord, such impulses being dis- 

 tributed by the thalamo- cortical fibres, the axones of the thalamic cells, to the 



