84 ESSENTIALS OF PHYSIOLOGY. 



lobe run in the internal capsule behind the auditory radiation, and are 

 joined by other fibres from the external geniculate body to form the 

 optic radiation. 



Some of the fibres of the superior cerebellar peduncle have cell 

 stations in the thalamus, but others are believed to pass through the 

 posterior end of the internal capsule without interruption to end in 

 the cortex in the neighbourhood of the central sulcus or fissure of 

 Rolando. 



The Association Fibres. The short association fibres lie immediately 

 under the cortex and connect the grey matter of adjacent convolutions. 

 The long association fibres form tracts which unite areas of the cortex 

 which are at some distance from each other. One tract, the superior 

 longitudinal fasciculus, runs between the frontal and occipital lobes ; 

 another, the inferior longitudinal fasciculus, connects the temporal and 

 occipital lobes ; a third, the uncinate fasciculus, connects the frontal 

 and temporal lobes ; a fourth connects the parietal and occipital lobes ; 

 while a fifth runs from the anterior perforated space (substance) over 

 the corpus callosum to the hippocampus. 



The commismral fibres connect the two cerebral hemispheres and 

 are grouped in the corpus callosum, and the anterior, posterior, and 

 hippocampal commissures. The corpus callosum contains fibres from 

 all parts of each cerebral hemisphere except the olfactory bulb and 

 parts of the temporal lobe. The olfactory lobes are connected by the 

 anterior and hippocampal commissures, the anterior commissure also 

 containing fibres which connect the two temporal lobes. The relation- 

 ships of the posterior commissure are unknown. 



The association and commissural fibres are either axons of cells in 

 the grey matter of the cortex or collaterals from axons ; they terminate 

 by arborisation in relation with other nerve cells. 



THE FUNCTIONS OF THE CEREBRAL HEMISPHERES. 



The ascent of the animal scale is marked by a progressive increase 

 in the size and development of the cerebral hemispheres, and in man 

 these structures are absolutely and relatively larger than in any of the 

 lower animals. This increase in size is associated with a corresponding 

 increase in functional importance, the higher centres acquiring a more 

 marked control over those in the spinal cord. This fact becomes more 

 apparent when the results of removal of the cerebral hemispheres in 

 different animals are compared. In the case of the frog, when the 

 animal has recovered from the shock of the operation, there is at first 

 sight little difference from the normal condition. The posture is 

 normal, equilibrium is maintained, and is regained if the frog is placed 



