THE INTEEBEAIN OR THALAMENOEPHALON. 



133 



nucleus and some farther away, numerous apparently similar cells, -which 

 surround all of the other more clearly defined nuclei. I will designate the 

 whole as the Nuc. diffusus thalami. 



As was already mentioned, nearly the whole external surface of the 

 thalamus is covered by the descending fibers of the optic tract. Between 

 the optic tract and the two described thalamic ganglia lies a double gan- 

 glion-complex, which is very constant and is, indeed, to be reckoned in 

 with the fundamental ganglia of the opticus system: the Corpus genic- 

 ulaium laterale (Figs. 81, 82, 83, and 84). It is present in all vertebrates. 

 In reptiles the author differentiates an antero-ventral from a postero-dorsal 



Tela chorioid. 

 Gangl. habeuulee 



3 parts of the Tfenia 



Genioulat. lat. dors. 

 Nucleus rotundus 

 Median nucleus 

 Opticus 

 ■T ~ Geaic. lat. ventr. 

 — Tr. strio-thal. dors. 

 - Stilus Corp. genie. 



'^_ Tr. strio-thal. ventr. 



Nucl. magno-cell. strat. gris 

 ... Basal optic root 



Fig. 82. — Frontal section through the Thalamus opticus of a young alligator. 



portion (see Fig. 82). It is possible that the latter merges into what in 

 man is called the Corpus geniculatum mediale. At least an analogously 

 located line may be seen in birds arising from the Decussatio transversa 

 and which may, in mammals, be followed as far as to and into the Gen- 

 iculatum mediale. There arises from the Corpus geniculatum laterale — 

 probably also from the Corp. genie, med. — a posteriorly directed Stilus 

 Corp. geniculati, which is lost in the posterior portion of the midbrain-roof, 

 possibly communicating, on the way, with the nucleus prsetectalis, later to 

 be described. In birds with enormously developed geniculatum it is very 

 large. 



