ASSOCIATION-FIBRES. 



165 



directed forwards. It is the principal cerebral commissure in all vertebrates below 

 mammals : the corpus callosum first making its appearance in the lowest mammals 

 and becoming developed proportionately with the increase of the mantle. 



The rope-like twist of the anterior commissure is associated by Hill with a rotation of 

 the cerebrum, which has occurred in the course of its development (Appendix A to English 

 Translation of Obersteiner's " Anatomy of the Central Nervous Organs "). 



3. The association-fibres which connect different parts of the same hemi- 

 sphere are either short or long. The short association-fibres (fibrce propria, Meynert ; 



Fig. 113. HORIZONTAL SECTION OF THE LEFT HEMISPHERE, 



SHOWING THE COURSE OF THE ANTERIOR COMMISSURE. 



(Testut). 



1, 2, anterior commissure ; 3, pillars of fornix ; 4, lateral 

 ventricle, anterior horn ; 5, lateral ventricle, descending 

 horn ; 6, 6', corpus striatum, caudate and lenticular nuclei ; 

 7, thalamus ; 8, internal capsule ; 8', anterior segment of 

 internal capsule. 



lamina arcuatce gyrorum, Arnold) (fig. 114, s.}, 

 serve to connect adjacent convolutions, passing 

 round below the grey matter at the bottom of the 

 fissures. The long association-fibres are mostly 

 collected into definite bundles, which can be 

 traced for a considerable distance between the 

 bundles of comrnissural and projection-fibres, or 

 which run free for a certain part of their course. 

 The principal bundles or tracts of long associa- 

 tion-fibres are the following : 



(a) Superior association - bundle (superior 



longitudinal fasciculus, fasciculus arcuatus, Burdach). This consists of sagittal fibres, 

 which run below the grey matter of the convex surface of the hemisphere, between 

 the frontal and occipital lobes, and between the frontal lobe and external part of the 

 temporal lobe (fig. 114,/J.s.). 



(b) Inferior association-bundle (temporo-occipital bundle, inferior longitudinal 

 fasciculus). This is a bundle of fibres which lies close to the outer wall of the 

 posterior and inferior cornua of the lateral ventricle and connects the temporal and 

 occipital lobes (f.Li.). 



(c) Anterior association-bundle (uncinate fasciculus). Under this name is 

 described a white bundle, seen on the lower aspect of the hemisphere, passing across 

 the bottom of the Sylvian fissure at the limen insulse, and connecting the frontal 

 with the temporal lobe (f.u.). The fibres of this bundle expand at each extremity, 

 and the more superficial of them are curved or hooked sharply between the con- 

 tiguous parts of the two lobes, from which circumstance it has derived the name 

 uncinate. Its fibres appear especially to connect the third frontal gyms with the 

 temporal lobe and with the anterior part of the limbic lobe. 



(d) Cingulum (ci.}. This forms the principal association-bundle of the gyrus 

 fornicatus, its fibres coursing immediately above the transverse fibres of the corpus 

 callosum, and passing from the anterior perforated space in front, curve round the 

 splenium of the callosum behind, and pass in the gyrus hippocampi as far as its 

 anterior extremity. Some of the fibres diverge, as they pass backwards, into the 

 white matter of the hemisphere, and probably reach various parts of the cortex. 

 The constitution of this bundle and its connections have been already dealt with 

 (see p. 158). 



(e) The perpendicular fasciculus (Wernicke), which runs vertically immediately 



