186 Proceedings of the Royal Irish Academy. 



These results are confirmed by recent obsei'vations of Pusateri^, who 

 found degenerations in these tracts after remoyal of portions of Munk's 

 auditory sphere in cats. 



It must, I think, therefore be unquestionably accepted that the 

 inferior longitudinal fasciculus is mainly, if not wholly, an association 

 link between the occipital and temporal lobes. This, the usually 

 accepted view, has recently been contested by Fleclmg"'^ who regards it 

 as a projection bundle, descending from the occipital lobe. It has, 

 however, on the other hand received confirmation from researches by 

 8aclis' into degenerations following softening of cii'cumscribed areas of 

 the cortex. 



2. Commismral Fihres : — 



(ff) Corpus callosum. — In every case degenerated fibres were traced 

 over the ventricular cavity towards the corpus callosum, across the 

 posterior half of which they passed to reach the opposite side (see 

 d. 5. fig. 1). In this commissiu'e, they were found mostly to occupy 

 the lower half of the vertical section. Having gained the opposite 

 side, a number were seen to bend downwards and radiate into the cortex 

 of the opposite temporal lobe. Some fibres turned forwards into the 

 internal capsule. These will be referred to later. 



But fibres of another set were also traceable from the seat of the 

 lesion totvards the region of the corpus callosum at its hinder part. 

 Here they entered the buudle of fibres known as the tapetum (see d. 

 3, fig. 3), and at once separated into two gi'oups. One of these re- 

 mained on the side proximal to the lesion, and passed back into the 

 occipital lobe, forming a layer immediately outside the posterior horn 

 of the lateral ventricle. The other crossed over in the corpus callosum, 

 and was found in the tapetum of the opposite side, along which its 

 fibres were traced backwards and downwards into the occipital lobe, 

 forming here also a layer placed closely external to the posterior horn 

 (see d. 4, fig- 4), and internal to the so-called optic radiations of the 

 white centre. In this way a communication is established between a 

 given area of temporal cortex and the surfaces of both occipital lobes. 



1 Pusateri, H.," Contrib. alio studio dell' origine del fascio pedunc. di Tiirck e del 

 fascio long, infer." II Pisani, s. 141—154. 



~ Flechsiff, P., "Die Localisation d. geistigen Vorgange, insbesond. der Sinnes- 

 Empfindungen d. Menseben." Leipz., 1896. 



=* Sachs, H., "Ueber Flechsig's Yerstand-Centren." Arcbiv f. Mik. Anat.,:B. 

 48, p. 550-572. 



