188 Proceedings of the Royal Irish Academy. 



passing from the coi-pus callostun into tlie internal capsule. Lejerine^, 

 howcTer, identifies it with, the occipito-frontal fasciculus of ForeP and. 

 Onufrowic%; but while denying that it receives any fibres from the 

 corpns callosmn, or contributes any to the internal capsule, admits 

 that it is made up of fibres fi'om two different souix-es. Where the 

 second set of fibres originates Dejeiine does not state. Mmgazzini^ 

 corroborates the view that the tapetum contains two sets of fibres, one 

 of which belongs to the fascicnlns occipito-frontalis ; the other is 

 furnished by the coi-pus callosnm. DoUo and Pusateri^ have also 

 found that the coi^dus callosum contributes fibres to the tapetum. ]\Iy 

 own results fully substantiate this latter view, and fui'ther show at 

 least one source fi-om which the callosal fibres come. They do not 

 lend any support to the belief that fibres of the tapetum descend into 

 the internal capsule. 



(h) Anterior commissure. — In all cases where the lesion of the 

 temporal cortex was extensive, marked degeneration was found in the 

 anterior commissui'e. Here the fibres occupied the inferior half of its 

 vertical section (Pars corticalis) (see d. 3. fig. 5), and passed across to 

 the opposite side, where they bent outwai'ds and backwai'ds, to end in 

 the lower and front part of the cortex of the temporal lobe. To reach 

 the anterior commissure, these degenerated fibres coursed fi'om the 

 seat of lesion, along the external capsule (see d. 8, fig. 4). But all 

 of those found in the external capsule did not enter the anterior 

 commissure. Many descended to the anterior and lower part of the 

 temporal cortex on the side of the lesion. Thi-ough the external cap- 

 sule and anterior commissure another bilateral connexion is thus 

 established between the cortex of the temporal lobe and both hemi- 

 spheres, comparable to that foinied in a posterior direction by the 

 fibres of the tapetum. 



(c) Fornix. — In a small number of the brains examined, degenerated 

 fibres were detected in the body of the fornix (see d. 6. fig. 4). They 

 probably belonged to the set of fibres described by authors under the 

 name of fasciculus perieavitarius medialis. They were traced forwards 



^ Dejerine, J., Anatomie des Centres Xerveux. Tome 1, p. 760. Paris, lS9o. 



- Forel, "Fall von Mangel d. Balkens in einem. Idiotenbim," Tagebl. d. o4. 

 Yersamml. deutsch. Naturforscli. u. Aertzte in Salzburg, ISSl. 



2 Mingazzini, G., " Osservaz. Amat. intom al corpo callose e ad alcuno formaz 

 clie con esse hanjio rapporto." Eicercli. lab. di Anat. Norm. TJniv. Eoma., vol. 

 vii., p. 0-28. 



^ Botio and Pusateri, " Sul decorso deUe fibs, del coiix callos. e del psalteruin." 

 Eivist. di patol. Xeiv e ment. ii., 2, 1897. 



