580 NERVOUS SYSTEM 



tant, are found in the tenia semicircularis, the uncinate fasciculus, the 

 fillet of the gyrus fornicatus and the inferior longitudinal fasciculus. 

 The last-mentioned fasciculus connects the gray matter of the tem- 

 poro-sphenoidal and occipital lobes. 1 



4. Fibres connecting the Brain with the Spinal Cord. Arising 

 from the internal concave surface of the cortical substance of the 

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

 curved commissural fibres, separate as the latter 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 converging 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 fasciculi which con- 

 verge to the gray substance of the corpora striata. The fibres from the 

 middle portion converge regularly to the middle region of the external 

 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 middle and anterior portions of the cerebrum, 

 especially 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 

 middle and anterior fibres undergo descending degenerations following 

 lesions of motor areas. A few of the converging fibres from the hemi- 

 spheres pass directly through the internal capsule and have no connec- 

 tion with the corpora striata and optic thalami. 



1 Recent researches by Flechsig, made by a new process called the embryclogical method, 

 though incomplete, probably will lead to important results. It has been ascertained that vari- 

 ous tracts of fibres receive medullary sheaths at different stages of intra-uterine development, 

 the axis-cylinders appearing first without coverings. As the medullary substance appears, the 

 fibres are said to become " myelinated." Association fibres are myelinated later than projec- 

 tion fibres, the latter receiving the sheath at about the fifth month. In studying embryos by this 

 method, Flechsig assumes to have demonstrated the exact course of various association tracts 

 and their connections with " association centres." The theoretical deduction from these ob- 

 servations are interesting, but can not as yet be accepted as conclusive. They relate largely to 

 the voluntary action of groups of muscles following sensory impressions of various kinds, cutane- 

 ous, auditory, visual, etc. 



