CONNECTIONS OF CORTEX WITH LOWER CENTRES. 781 



quadrigemina ; these probably chiefly serve to carry impulses for reflex move- 

 ments of the eye. 



Loss of the eyes in a new-born pup is followed by diminished development 

 (atrophy) of the optic nerves and tracts, of the occipital lobes, of the superficial 

 white matter of the anterior corpora quadrigemina, of the corpora geniculata 

 lateralia, and of the pulvinares thalami, 1 but not of the mesial corpora genicu- 

 lata nor of the posterior corpora quadrigemina. 



Connections of the auditory area. — Lesions of the first and second 

 temporal gyrus are followed by descending degenerations in the part of the 

 internal capsule which lies ventral to the lenticular nucleus and in the 

 outermost part of the crusta. 2 These fibres terminate in the nuclei pontis. 

 There are also commissural fibres passing by way of the corpus callosum to the 

 temporal and to the occipital lobes of the opposite hemisphere (Sachs), 

 and association fibres passing into the angular gyrus, and into the occipital lobe 

 of the same hemisphere, and probably also into the Rolandic area and towards 

 the speech centre. The course of these last has, however, not as yet been 

 definitely traced. Ferrier and Turner found no degeneration in the posterior 

 quadrigemina! bodies, nor in the fillet, after lesions of the first temporal gyrus ; 

 v. Monakow, in experiments upon young animals, found atrophy of the 

 mesial geniculate body to follow destruction of this convolution. 



The corticipetal tract from the peripheral sense organ to the auditory area 

 of the cortex, passes by the cochlear nerve to the auditory nucleus ; other fibres 

 arising thence probably terminate in the superior olive, the nucleus of the 

 fillet, the posterior corpus quadrigeminum, and the mesial geniculate body of 

 the opposite side ; and others again, starting from these nuclei, carry the tract 

 on to the cortex of the temporal lobe. 



Connections of the olfactory region of the cortex. — The olfactory 

 lobe (including the olfactory bulb and tract, and the part of the frontal 

 lobe near the attachment of the olfactory tract) 3 is connected with the two 

 extremities of the limbic lobe. Fibres from the olfactory lobe pass by means 

 of the outer root of the tract to the anterior part of the hippocampal gyrus, 

 and other fibres have been traced from it into the fascia dentata. The inner root 

 is connected with the anterior end of the gyrus fornicatus. Some of its fibres 

 were described by Meynert as passing by way of the anterior commissure to the 

 temporal lobe and hippocampal region of the opposite side, but the evidence 

 of this " olfactory chiasma " is insufficient. There is, however, as Ganser has 

 shown, a commissural connection between the two olfactory regions of the 

 cortex by means of the anterior commissure. These connections have been 

 already noticed (see p. 764). There is, further, an important association 

 bundle in connection with this region in the cingulum, which courses in the 

 white matter of the gyrus fornicatus and gyrus hippocampi ; its fibres probably 

 connect those gyri with the cortex of the outer surface of the hemisphere 

 (Beevor). 4 Zuckerkandl 5 has described a bundle of association fibres in the 

 body of the fornix connecting the cornu ammonis with the temporal and 

 olfactory lobes. 6 The hippocampi of opposite sides are said to be connected 

 commissurally by the " lyra." The fornix further carries fibres from the 

 hippocampus to the corpus albicans. Most of these end here, but some are 

 said to pass to the opposite side and to end in the grey matter of the third 



1 v. Gudden, Arch. f. Ophth., Leipzig, Bde. xx., xxi., xxv. ; Tar/cbl. d. 58 Versamml. 

 deutsch. Naturf. u. Acrztc in Strassburg, 1885; v. Monakow, Arch. f. Physiol., Leipzig, 

 1885, S. 329 ; Arch. f. Psychiat., Berlin, Bde. xiv., xvi., xx., xxiii., xxiv. 



- Zacher, Arch. f. Psychiat., Berlin, Bd. xxii. S. 654; Flechsig, op. cit.; Ferrier and 

 Turner, op. cit. 



3 See Quain's "Anatomy," vol. iii. pt. 1, p. 159. 



4 Phil. Trans., London, 1891, B, p. 135. 



5 " Das Riechbundel des Aininonshorns," A vat. Anz., Jena, 1888, Bd. iii. S. 15. 



6 See on the subject of the connections of the hippocampus with other parts, M. et Mine. 

 Dejerine, Compt. rend. Soc. do biol., Paris, 1897, p. 587. 



