i6o 



CHORDATE ANATOMY 



diencephalon. The paired ventricles are nearly obliterated by the enlarge- 

 ment of the striate bodies, archistriatum and neostriatum. For the 

 first time in the vertebrate series, a cortical layer of pyramidal cells 

 appears in the pallium, having nervous connexions with fibers of the 

 olfactory tract. Septum and hippocampus appear in the medial wall 

 much as in Amphibia. The dorsal wall of each hemisphere is homologized 

 with the gyrus dentatus of the mammalian brain. The transitional 



Fig. 319. — Brain of goose, ac, anterior commissure; cb, cerebellum; e, epiphysis; 

 /, flocculus; h, hypophysis; hs, hyperstriatum; i, infundibuluni; /, lateral ventricle; m, 

 medulla oblongata; ms, mesostriatum; ob, olfactory bulb; ol, optic lobe; s, striatum; 

 i, temporal lobe; III, third ventricle; x, plane of section E. (From Kingsley's "Com- 

 parative Anatomy of Vertebrates," after Butschli.) 



region between this dorsal pallium and the neostriatum has important 

 potentialities, since it is unconnected with olfactory fibers, and since in 

 mammals it becomes the neopallium from which develops the greater part 

 of the cerebral cortex on which the higher psychic activities of man 

 depend. (Figs. 318, 324) 



In the region of the diencephalon of lizards the anterior epiphysial 

 outgrowth, the parietal organ, develops a lens, retinal and pigment layers, 

 and nerve fibers which are connected with centers in the brain wall. 

 It is therefore, so far as its structure goes, an eye. The thalamic thicken- 

 ings of the lateral wall divide the third ventricle into a dorsal and ventral 

 cavity connected by a narrow slit-like passage. In snakes the optic lobes 



