916 



THALAMUS OPTICUS. 



animals in which the visual axes are parallel, e.g. man. Paths of which the 

 functions are less well indicated than the above run to the homonymous and 

 contralateral corpora striata, to the homouymous half of the cerebellum, to the 

 motor nuclei of the bulb, chiefly of the crossed side. 1 The mesencephalon 

 also receives a path from the corpus striatum, 2 but in the bird none from the 

 pallium (cortex cerebri). 3 



THE DlENCEPHALON OR EEGION OF THE THALAMUS OPTICUS. 



This region includes as its main divisions, studied in regard to func- 

 tion, the optic thalamus, subthalamic body, and lateral geniculate body. 

 The two latter bodies may be considered grey nuclei somewhat more 

 definitely separable than, but otherwise comparable with, the remains of 

 some twenty (Nissl, v. Monakow) grey nuclei composing the thalamus. Of 

 the first and last named only, has more definite knowledge been acquired. 

 The region relatively to its bulk sends but very few fibres in a caudal 

 direction ; on the other hand, it is an abundant source of fibres passing 

 into the telencephalon (both corpus striatum and cortex). It is con- 

 nected with the Rolandic region of the cortex by a system of fibres that, 

 among cortical fibres, become myelinated somewhat early (ninth foetal 

 month), and by later developing systems with (1) The gyrus hippo- 

 campi, cingulum, and gyrus fornicatus (first post-natal month), and (2) 

 with the frontal convolutions (fourth post-natal month). It is also 

 connected with the cortex of the insular region, and sends an especially 

 numerous fibre system to the occipital and temporal cortex, including 

 pre-eminently that of the calcarine and angular gyri. The researches of 

 Dejerine 4 prove that there is practically no region of the cortex of the 

 hemisphere which does not receive nerve fibres from the optic thalamus, 

 and that, on the other hand, there are no fibres from the thalamus to the 

 pes pedunculi cerebri. 



Panizza 5 and Jos. Swan 6 almost simultaneously discovered that 

 destruction of an eye is followed by shrinkage of the contralateral optic 

 thalamus. In the lower vertebrata the corpora bigemina are the chief 

 regions of reception of the fibres of the optic " nerve." In the higher 

 mammalia diencephalic nuclei of ending of the optic nerves assume 

 larger and larger proportions as compared with mesencephalic. 7 In the 

 rabbit the main nucleus is still the anterior corpus quadrigeminum ; in 

 man the lateral geniculate body preponderates. Only in primates is 

 the pulvinar large ; in other mammalia it is small. All goes to indicate 

 the growing importance of the cortical mechanism concerned with vision 

 in the evolution of the sense. Of the four masses of grey matter into 

 which in mammals the thalamus is broadly and easily divisible, it is the 

 hindmost (pulvinar) that is directly in receipt of fibres from the optic 



1 Miinzerand Wiener, Monatschr. f. Psychiat. u. NeuroL, Berlin, 1898, Bd. iii. 



2 Edinger, " Vorlesungen ueber d. Bau d. nerv. Centralorg.," 1896, 5te Aufl. ; Mtinzer 

 and Wiener, loc. cit. 



3 Edinger, Miinzer and Wiener, Boyce and Warrington. 



4 Compt. rend. Soc. de bioL, Paris, 1893, p. 193; ibid., Feb. 1897; also 1898 with 

 E. Long; also Dejerine's "Anat. d. centres nerveux," Paris, 1894. 



5 Mem. r. 1st. Lomb. di sc. e lett., Milano, 1856. tomo v. p. 375; " Observations sul 

 nervo ottico," April 19, 1855 (bird and man). Panizza also drew attention in this 

 same memoir to the fact that an atrophy of the occipital region of the cortex, and in 

 less degree of part of the parietal, ensues in man on loss of an eye in childhood. 



6 " On the Origin of the Optic Nerve," London, 1856. The observation is on the horse, 

 pi. viii. fig. 5. 



7 Gudden, Ganser, Monakow, Edinger, etc. 



