2 Journal of Comparative Neurology. 



of Meynert, in 1872,1 and accepted as an inaugural discussion 

 by the University of Zurich. I wish to give here a short sketch 

 of the ground which this paper covers, as it is not easy to get 

 it in the original. The optic thalamus of the lower mammals 

 differs from that of man and of the monkey by a gradual de- 

 crease of the pulvinar, which is very short in the carnivora and 

 can be considered to be absent in the ungulata and rodents. 

 The thalamus is however even shorter in the lower mammals 

 than it seems to be, as what appears to be its posterior part, is 

 formed by an unproportionately large external geniculate body, 

 which reaches the upper surface of the thalamus. The small 

 cuneiform external geniculate body of man is much more inde- 

 pendent from the thalamus, and it is easy to see why it was not 

 recognized in the lower mammals, although it is much larger : it 

 is too little marked off from the thalamus. In the carnivores 

 the external geniculate body is right above the internal one; in the 

 rodents, in which the thalamus is even shorter than in the carni- 

 vora, the internal geniculate body is situated caudad of the exter- 

 nal geniculate body. The fibres of the optic tract which pass 

 through the external geniculate body to the corpus guadrigemi- 

 num anterius are covered in man by the pulvinar thalami, but 

 are superficial in the lower mammals, where the pulvinar is not 

 developed. The stratum zonale thalami of man is therefore 

 different from what might be called stratum zonale thalami in 

 lower mammals, where the superficial layer in the posterior part 

 of the thalamus is formed by fibres of the optic tract passing 

 through the superficial corpus geniculatum externum. — There 

 are other points which help to explain the difference in the in- 

 ternal structure of the optic thalamus in man and in lower 

 mammals. In the latter the hemispheres are small; the corona 

 radiata is correspondingly small and covers only the anterior 

 part of the optic thalamus leaving the posterior part free. This 

 is why the fibries of the corona radiata do not show as a 



I. Beitrage zur Kenntniss des Thalamus opticus und der ihn umgebenden 

 Gebilde bei den Saugetieren, von August Forel aus Waadt. Kaiserl. Academic 

 der Wissenschaften in Wien, 1872. No. XVI. Math-naturwiss. Classe. 6 Juni. 

 Ueberreicht von Prof. Dr. Th. Meynert. 



