DIRECTION OF THE FIBRES IN THE CEREBRUM. 611 



also the corpora striata, on the two sides. (C) Fibres from the deeper portion 

 of the crus cerebri (tegmentum) pass to the optic thalamus on either side and 

 thence to the temporo-sphenoidal lobes. These fibres form the posterior com- 

 missure and connect the temporo-sphenoidal lobes and the optic thalami of 

 the two sides. 



3. Fibres connecting Different Cerebral Convolutions on the same Side. 

 (A) The so-called arcuate fibres, passing in a curved direction from one con- 

 volution to another, connect adjacent convolutions. (B) Other fibres, called 

 longitudinal or collateral fibres, connect distant convolutions with each other. 

 The fibres of the fornix connect the optic thalamus with the hippocampus 

 major and the unicate gyrus. Fibres in the corpus callosum connect the an- 

 terior and posterior extremities of the gyrus f ornicatus. These are the longi- 

 tudinal fibres of the corpus callosum. Other longitudinal fibres, connecting 

 parts more or less distant from each other, are found in the tsenia semicircu- 

 laris, the unicate fasciculus, the fillet of the gyrus fornicatus and the inferior 

 longitudinal fasciculus. The last-mentioned fasciculus connects the gray 

 matter of the temporo-sphenoidal and occipital lobes. 



4. Fibres connecting the Brain ivith the Spinal Cord. If these fibres be 

 followed from the cortex of the brain downward, they are called converg- 

 ing, and if they be followed from below upward, they are called radiating 

 fibres. 



Arising from the internal, concave surface of the cortical substance of the 

 cerebrum, the converging fibres, at first running side by side with the curved, 

 commissural fibres, separate from the latter as they curve backward to pass 

 again to the cortical substance, and are directed toward the corpora striata 

 and the optic thalami. The limits of the irregular planes of .separation of 

 the commissural and the converging fibres contribute to form the boundaries 

 of the ventricular cavities of the brain. In studying the course of the con- 

 verging fibres arising from all points in the concave surface of the cerebral 

 gray matter, it is found that they take various directions. The fibres from 

 the anterior region of the cerebrum pass backward and form distinct fascic- 

 uli which converge to the gray substance of the corpora striata. The fibres 

 from the middle portion converge regularly to the middle region of the ex- 

 ternal portions of the optic thalami. The fibres from the posterior portion 

 pass from behind forward and are distributed in the posterior portion of the 

 optic thalami. The fibres from the convolutions of the hippocampi and the 

 fascia dentata are lost in the gray substance lining the internal borders of 

 the optic thalami In the course of most of these fibres toward the corpora 

 striata and the optic thalami, they pass through the internal capsule. 



The fibres from the anterior and middle portions of the cerebrum, espe- 

 cially the middle portion, contribute largely to the formation of the anterior 

 two-thirds of the posterior division of the internal capsule. The fibres from 

 the posterior portion of the cerebrum are found in the posterior third of the 

 posterior division of the internal capsule. The posterior fibres are probably 

 sensory. The middle and anterior fibres are motor. The latter undergo de- 

 scending degenerations following lesions of the anterior and posterior central 



