a 
548 THE NERVOUS SYSTEM. 
the cortex of the same hemisphere. They are grouped into long and short associa- 
tion bundles. 
The greater number of the short association fibres pass between adjacent 
convolutions. They curve round the bottom of the sulci in U-shaped loops. Some 
of these occupy the deepest part of the gray cortex itself, and are termed intracortical 
association fibres (Fig. 405, p. 544); others he immediately subjacent to the gray 
matter—between it and the general mass of the white matter—and receive the 
name of subcortical fibres. Many groups of short association fibres, instead of linking 
together contiguous convolutions, pass between gyri more or less remote. It is only 
after birth, when intellectual effort and education have stimulated different portions 
of the cortex to act in harmony and in conjunction with each other, that these 
association fibres assume their sheaths of medulla and become functional. 
The long association fibres are arranged in bundles which run for considerable 
distances within the white medullary centre of the cerebral hemisphere, and unite 
districts of gray cortex which may be far removed from each other. The better 
known of these fasciculi are the following: (1) the uncinate; (2) the cingulum ; 
(3) the superior longitudinal; (4) the inferior longitudinal ; (5) the occipito- frontal. 
The fasciculus uncinatus is composed of fibres which arch over the stem of the 
Sylvian fissure and connect the frontal pole, and the orbital convolutions of the 
frontal lobe, with the front portion of the temporal lobe. 
The cingulum is a very well-marked and distinct band, which is closely associated 
with the limbic lobe. Beginning in front, in the region of the anterior perforated 
spot, it arches round the genu of the corpus callosum and is carried backwards on 
the upper surface of this structure at the place where its fibres pass into the 
ASSOCIATION FIBRES ~ iY , ASSOCIATION 
><FI 
Fic. 408.—DIAGRAM OF THE LEADING ASSOCIATION BUNDLES OF THE CEREBRAL HEMISPHERE. 
(Founded on the drawings of Déjerine.) 
A. Outer aspect of hemisphere. B. Inner aspect of hemisphere. 
callosal radiation. The cingulum, therefore, hes under cover of the callosal gyrus 
and stands in intimate relation to the white centre of this convolution (Fig. 392, 
p. 529). At the hinder end of the corpus callosum the cingulum turns round 
the splenium and is carried forwards, in relation to the hippocampal gyrus, to the 
uncus and the temporal pole. The cingulum is composed of several systems of 
fibres which only run for short distances within it. 
The fasciculus longitudinalis superior is an arcuate bundle which is placed on the 
outer aspect of the foot or basal part of the corona radiata and connects the frontal, 
occipital, and temporal regions of the hemisphere. It lies in the base of the fronto- 
parietal operculum and sweeps backwards over the insular region to the posterior 
end of the Sylvian fissure. Here it bends downwards round the hinder end of the 
putamen and proceeds forwards in the temporal lobe, to reach its anterior extremity. 
As it turns downwards to reach the temporal lobe numerous fibres radiate from it 
into the occipital lobe. 
The fasciculus longitudinalis inferior is a very conspicuous bundle which extends 
along the whole length of the occipital and temporal lobes (Fig. 392, p. 529). In the 
occipital lobe itis placed on the outer aspect of the optic radiation, which takes a similar 
direction and from which it is distinguished by the greater coarseness of its fibres 
(Figs. 397, p. 535; 400, p. 538; 409, p. 550). It is not present in the macaque 
monkey (Ferrier and Turner), but is well developed in the orang and the chimpanzee. 
