j6 Journal of Comparative Neurology 



vessels renders difficult the removal of this membrane from the 

 thin walled portion of the brain. 



General Form of the Brain. — The brain of CJiclydra as a 

 whole, seen from the dorsal aspect, is very long in proportion 

 to its width, the length being to the width as three and one half 

 to one, measured in the maximum direction — i.e. from the 

 cephalic end of the olfactory lobes to the caudal end of the ob- 

 longata, and directly across the cerebrum at its widest part. 

 This ratio is greater than that in the brain of any other reptile 

 that I have examined. Agassiz (i) gives the ratio of the length 

 to the width of the brain in the Testudianata as about 2 to I. 

 The relative cephalo-caudal length of the segments, measured 

 from the dorsal aspect is seen in the table below. The dien- 

 cephal is not included as it is almost completely hidden by the 

 overlapping cerebrum. The measurements fail to give the exact 

 relative size of the parts, especially in the epencephal, as the 

 cerebellar portion of this segment is sharply curved. The curve 

 of the metencephal is not great enough to make much differ- 

 ence. The measurements are from an adult turtle, one with a 

 carapace about 36 centimeters in length. At the suggestion of 

 Prof. Wilder the relative length of each segment is given taking 

 the mesencephal as the standard as it is the most constant in size 

 of the segments and attains more nearly the same development 

 in all forms. 



Brain Measurements. 



Length Rel. Length Width 



Encephalon 32 mm. 5.3 



Rhinencephal 6 " I. 5.3 mm. 



Prosencephal 9 " 1-5 9- " 



Mesencephal 6 " 1. 6.3 " 



Epencephal , 4 " .66 4. " 



Metencephal 9 " 1.5 6. " 



From a lateral view (Fig. 3) the brain of the adult shows 

 less flexure of the oblongata than is usual in Chelonia, and also 

 shows its great length in comparison with its dorso-ventral dia- 

 meter. On the dorsal surface, lying between the caudal por- 

 tions of the cerebral hemispheres is a structure having a curved 



