100 PHYSIOLOGICAL SBRIES. 



owe their size mainly to the great development o the 

 valvula cerebelli. Their roof is composed as usual of two 

 ehiel' layers an outer cellular and fibrous layer from 

 which the optic tracts arise, and an inner commissural 

 laver; but the outer layer is deficient over a large triangular 

 in the iniil-dorsal parts, leaving a semitransparent 

 membrane (the commissural layer) through which the 

 wings of the valvula cerebelli can be seen (upon the right 



Fig. 28. 



CUT EDGE. LOB - FAC - 



/ CER. / 



LOB. VAC. 



--VALV.CER. 



TECT. OPT. 



Brain of Cyprinus carpio. 



-ide black paper has been inserted beneath a part of this 

 exposed commissural layer). The epiphysis is small and 

 pear-shaped. The olfactory bulbs are situated close to the 

 olfactory organs. The olfactory peduncles are somewhat 

 widely separate, but are connected, as far as the bulbs, both 

 dorsally and ventrajly by a delicate membrane (black 

 |.;I|HT ii inserted beneath its anterior end), the upper layer 

 of which is a forward extension of the pallium. 



D. 108. The head of a Tench ( Tinea vulgaris) exposed from above. 

 This brain has the same general characters as that of the 

 <'arp, but differs from it in the smaller size and more 

 globular form of the cerebellum. The tectum opticum 

 also has only a small median area deficient in the outer 

 layer, from which as this deficiency is apparently due to 

 the thrusting aside of the lateral parts of the tectum by 

 the contained valvula cerebelli one may infer that the 

 valvula is less developed. 



Presented by T. W. II. Burne, Esq. 



D. 100. The isolated brain of a smaller Tench (Tinea vulgaris) . 

 This specimen is similar to the last, but, in addition, shows 



