44 JoURNAI. Ol- Cl)MI'\H\TI\ K XeUKOLOG^. 



equal. In all other cases, the breadth exceeds the len^thC) 

 (see Table II). 



HEMISPHERKS. 



As usual, the prosencephalon is composed of two hemi- 

 spheres, which are compressed against each other at the 

 meson. Each hemisphere is a gibbous sub-conical body, 

 with its apex directed cephalad and its base directed caudad. 

 The ventral surface of each hemisphere is undulating; the 

 lateral surface may be either longitudinally undulating or 

 convex; the mesal surface is flattened: the cephalic, dorsal 

 and caudal surfaces are convex. 



Connections. — At the meson, the hemispheres are sepa- 

 rated by a deep longitudinal fissure (Fissura longitudinalis). 

 The hemispheres are connected with each other by the 

 anterior commissure and the corpus callosum. The hemi- 

 spheres are connected with the diencephalon b\- the crura 

 cerebri. 



Dorsal aspect (Plate V, Figs. 5, 6, S, 10). — Viewed from 

 above, the outline of each hemisphere of the avian brain is 

 composed of the following elements: 



1. A short convex curve, which passes caudo-mesad from 

 the cephalic extremity of the hanisphere to the meson. 



2. A straight line, which continues this curve caudad 

 alonsf almost the entire mesal border. 



I The following tables show that there is a great resemblance between the brains of 

 American and of European birds. All these tables are translated from A. Bumm's work 

 on the avian prosencephalon Op. cit , p. 431-432. 



Table of ratios of the transi'erse to the longitudinal diameter of the avian prosen- 

 cephalon compiled by Leuret, after an examination of thirty-six species). — In the parrots, 

 I : I 09 ; in the swimming birds, i : 0.99 ; in the fringilline birds, i : 0.91 ; in the oscinine 

 birds, I : 0.81 ; in the wading birds, i : 0.79; in the fowls, i : 0.79; in the birds of prey, 

 I : 0.74 ; in the doves, i : o 74. 



Table of ratios of the ividth to the length of the avian Mesencephalon (compiled by 

 Serres, after the examination of thirty-one species). — In the parrots, i: i.oo; in the 

 oscinine birds, i : 0.85 ; in the wading birds, i : 0.85 ; in the swimming birds, i : 0.80 ; in 

 the running birds, i : 0.76 ; in the birds of prey, i : 0.70 ; in the fowls, i : 0.66. 



Table of ratios of the length to the depth of the avian prosencephalon compiled by 

 Serres). — In the fowls, i : 0.75 ; in the running birds, i : 0.69 ; in the birds of prey, i : 0.69 ; 

 in the swimming birds, i : 0.60; in the wading birds, i : 0.60; in the parrots, i : 0.59: in the 

 oscinine birds, 1 : 0.58. 



