CENTRAL NERVOUS SYSTEM 541 



responsibility for the integration of the very complex patterns of instinctive 

 behaviour characteristic of the higher Vertebrates. 



This is made clear by the researches of Briigger (1943), Hess and Briigger (1943) 

 and Hess (1943-44). Probing the hypothalamic region of cats with electrodes, they 

 found areas where the stimulus elicited complex patterns of behaviour in their entirety, 

 such as fighting, eating and sleeping, all displayed in perfect coordination. Thus 

 the cat looked around, searched for a suitable corner in which to go to sleep, and 

 forthwith went to sleep ; presumably felt hvmgry, searched for food, ate the food, 

 rested, and so on. Here, therefore, lie the anatomical bases of the centres controlling 

 the highest instinctive patterns, set between the receptors and effectors, combining 

 and assessing incoming impressions and redisiDatching instructions in an integrated 

 form, at the same time relaying on to the cortex those reqtiiring further analysis. 

 These thalamic centres control the lower centres and in higher animals are themselves 

 influenced and controlled by higher cortical centres, an effect seen, for example, in the 

 " sham rage " and evidences of general sympathetic hyperactivity that occur in the 

 cat after its cortico-thalamic connections have been cut (Bard, 1928 ; Cannon, 1929). 



The two nuclei derived from the thalamus with visual connections are 

 the lateral geniculate body and the pulvinar. 



THE LATERAL GENICULATE BODY. The aulagc of the lateral geniculate 

 body is evident even in the primitive Cyclostomes (Herrick and Obenchain, 

 1913) ; it is recognizable in most Fishes as a nest of cells in the angle between 

 the optic tract and the tectum (Franz. 1912). and is relatively well developed 

 in Teleosteans (Kappers, 1920). In Amphibians. Reptiles and Birds, it 

 remains small (see Kappers, 1921) and is not j^rojected onto the cortex 

 (Elliot Smith, 1928), but in Mammals it shows an abrupt development. It 

 is well represented among all Mammals excejDt semi-blind types such as 

 the mole (Gan.ser. 1882 ; Frankl-Hochwart. 1902). and it assumes many 

 variations of structure in the different species. ^ In the more primitive 

 Mammals (Marsupials) it has a dorsal and a ventral nucleus showing no 

 lamination, and lies vertically on the surface of the brain (Fig. 715). The 

 ventral nucleus is the more primitive and is homologous with the entire 

 geniculate body of Fishes, Reptiles and Birds : the dorsal nucleus only is 

 projected to the cortex.- As evolution proceeds, changes take place con- 

 sisting of a disappearance of the primitive ventral nucleus, the appearance 

 of rows of large cells along the periphery of the dorsal nucleus, and the 

 lateral rotation of the whole structure so that the original external surface 

 lies ventrally. Its highest differentiation is seen in the Primates, in which 

 it is represented almost entirely by the dorsal nucleus.^ In these the 

 primitive ventral nucleus has dwindled almost into insignificance ; it 

 probably receives only crossed optic fibres and none from the recently 

 developed macula (^Minkowski. 1920), and from it issues the brachium 



1 v. Monakow (1883). Cajal (1904), Sachs (1909), Xeiding (1911), Winkler and Potter 

 (1914), Horne-Craigie (192.5), Overbosch (1926). Putnam (1926)" Le Gros Clark and Penman 

 (1934), Packer (1941). Le Gros Clark (1941). 



2 v. Monakow (1883), Kappers (1920), Winkler (1921), Brouwer (1923), Putnam (1926). 



3 Ziehen (1903), Sachs (1909). Friedemann (1912), Minkowski (1913). 



