II22 



HUMAN ANATOMY 



and from whose cells corticipetal fibres pass to all parts of the cerebral cortex 

 and to the corpus striatum. Further, it must be understood that the thalamus 

 receives fibres from all parts of the cerebral cortex, and, lastly, that from it 

 proceed efferent fibres to the lower centres within the brain-stem and the cord. 

 It is evident, therefore, that the connections of the thalamus are very intricate 

 and far reaching. 



I. The lower thalamocipetal tracts include : (a) those passing directly from the spinal cord, 

 as the spino-thalajnic and possibly a part of Gowers' tract ; {b) those passing from the 

 various nuclei by way of the median fillet ; {c) those passing from the cerebellum, either 



directly, as the cerebello-thalamic 

 Fig. 969. tract, or, after interruption in the 



red nucleus, as the rubro-thala- 

 mic; (d) probably other tracts 

 w hich arise within the tegmen- 

 tal area of the brain-stem. The 

 fibres from the various sources 

 enter the under surface of the 

 thalamus to end within the ven- 

 tral nucleus, or by means of the 

 internal medullary lamina to be 

 distributed to the other nuclei. 



2. The thalamic radiation 

 comprises the fibres which stream 

 from the latero- ventral surface of 

 the thalamus to all parts of the 

 hemisphere ( thalarno-cortical), 

 some crossing by way of the 

 corpus callosum to the oppo- 

 site side, as well as those which 

 pass in the opposite direction 

 ( cortico-thalaniic ) towards the 

 ganglion. Although as they 

 traverse the external medullary 

 lamina the fibres are not particu- 

 larly grouped, their various rela- 

 tions to the cortex or other parts 

 are established by different and 

 more or less definite paths. 

 These are designated as the 

 stalks of the thalamus, of which 

 a frontal, a parietal, an occipital 

 and a ventral are conventionally 

 distinguished. The anterior or 

 frontal stalk emerges from the 

 fore-part of the lateral surface of 

 the thalamus, traverses the aii- 

 terior part of the internal capsule 

 between the caudate and lentic- 

 ular nuclei, to which it distributes 

 fibres, and finally gains the cortex of the frontal lobe. From the cells of this region, cortico- 

 thalamic fibres follow in reversed order the paths just mentioned, thus establishing a 

 double relation between the cortex and the basal ganglion. In addition to the preceding 

 cortico-thalamic fibres, the antero-ventral part of the thalamus receives a strand from the 

 cortex of the olfactory bulb. The parietal stalk leaves the lateral surface of the thalamus and 

 enters the internal capsule and often the lenticular nucleus, in its course to the parietal 

 cortex. Other corticipetal fibres, destined for the parietal and adjacent parts of the 

 frontal lobe, are the continuations of the path of the mesial fillet. To a large extent 

 these fibres pass from the ventral thalamic nucleus outward to the under surface of 

 the lenticular nucleus, then bend upward and traverse the lenticular nucleus by way of 

 the medullary striae or the globus pallidus to gain the cortex. Other fibres continue the fillet- 

 path by entering the internal capsule and thus, perhaps, directly proceed to the cortex. The 

 occipital stalk includes the fibres that connect the thalamus with the visual cortical areas of the 

 occipital and parietal lobes. They issue from the lateral surface of the pulvinar, and as the 



Rubro-thalamic 

 Cerebello-thalamic 



Median fillet 

 Spino-thalamic 



Diagram showing chief connections of thalamus ; black fibres rep- 

 resent afferent tracts ending in thalamus and thalamocortical paths ; 

 red fibres are the cortico-thalamic and strio-thalamic paths ; TV?, thal- 

 amus ; C, L, caudate and lenticular nuclei; C, C, corpus callosum; 

 /^, P, T, O, frontal, parietal, temporal and occipital lobes; /^:tr, fornix; 

 M, mammillary body ; Pd, cerebral peduncle; SC, IC\ superior and in- 

 ferior colliculi ; R, red nucleus; Ps, pons ; /, frontal stalk ; 2^ parietal 

 stalk ; J, 4, lenticular and temporal parts of ventral stalk ; 5, occipital 

 stalk. 



