NERVOUS SYSTEM 



165 



also is the corpus pineale of the birds ; it is either large and in 

 the form of a sac, or small and constructed of follicles, or quite 

 solid. In the embryos of certain swimming birds temporary 

 rudiments of a parietal spot are present in the form of a small 

 pigmental area, while only in the crested goose is the skull 

 perforated by a foramen parietale above the place of the 

 parietal organ. In mammals the parietal organ is a solid, 

 conical body, wherein but a proximate part of the earlier lumen 

 is present. A special peduncle is generally absent, except in 

 the common chimpanzee, where the conditions are still simpler 



FIG. 83. Sagittal section of the parietal eye, parietal nerves and distal extremity 

 of the epiphysis of an almost mature embryo of Hatteria punctata. (Oppel, 

 Vergl. mikr. Anat., Part v., Fig. 83.) Pa, Parietal eye; Npar. Parietal 

 nerve ; Ep, Epiphysis. 



than in man. 1 In man the upper surface of the organ is uneven, 

 in all other mammals it is smooth. 



The form of the parietal organ is liable to vary ; thus in 

 the pig it is spindle-shaped and elongated, in the sheep pear- 

 shaped, in the dog flat, and in man (see Fig. 84) conical, with the 

 apex directed backwards. The human pineal gland measures 

 sagitally 8-12 mm., transversally 6-8 mm., and is larger in the 

 female sex than in the male sex. but in the former weighs only 

 0*00012 per cent, of the entire weight of the cerebrum. 



J Studnicka, loc. cit., pp. 210-219. 



