1 62 THE HUMAN SPECIES 



the corpora callosa of the other mammals are thin. 1 In all 

 Vertebrates the medulla oblongata, originating in the fifth 

 cerebral vesicle, exists previous to the formation of the Pons 

 Varoli ; in proportion, however, as the matter increases, it being 

 the more vital part of the brain, the medulla oblongata is less 

 prominent.- 



Two peculiar cerebral formations which have recently aroused 

 special interest have still to be considered. These are the 

 hypophysis cerebri and the glandula pinealis. In man peculiar 

 conditions prevail with respect to the hypophysis. It is worthy 

 of remark that the cavity in the hypophysis, corresponding, to 

 a certain extent, to a sixth ventricle, has almost disappeared in 

 man, and the organ is comparatively small. 



Huschke 3 gives the following figures for the proportion of 

 the hypophysis cerebri to the cerebrum : 



In man = i 



beasts of prey = i 



the pig = i 



horse = i 



,, rodents = i 



ruminants = I 



2304 



723-960 



450 



352 



104-360 

 77-121 

 52-99 



birds = i 



In animals the hypophysis consists of an anterior lobe, 

 having the character of a vascular gland, and a small posterior 

 lobe of grey matter containing nerve fibres in its fine-grained, 

 nuclear tissue. Tumours and other diseases arising in the tissue 

 of the hypophysis are associated with the occurrence of acro- 

 megaly ; I do not know whether the same conditions have been 

 observed in animals. 



The glandula pinealis, which is situated on the anterior pair 

 of corpora quadrigemina, has from the earliest times attracted 

 the attention of anatomists far more than has the hypophysis ; 

 indeed, the philosopher Descartes 4 raised it to the dignity of 

 the seat of the soul. Although we can hardly attribute so great 

 a significance to it nowadays, it has attracted the notice of 

 anatomists from another point of view, in that it has been 



1 Huschke, loc. cit., p. no. *Ibid., p. 85. 3 Ibid., p. 106. 



4 Descartes, Les passions de I'dme, 1649. 



