88 ME. H. G. SEELET ON THE 



incli, wHle its greatest depth in the middle of each cerebral he- 

 misphere is about f^ of an inch. It has the outline shown 

 in ]P1. XI. fig. i. I regard the upper part of the outline as 

 showing that the cerebral hemispheres were divided from each 

 other, as among birds, by a deep impression of the parietal bones, 

 that they were convex from within outward, and deep from above 

 downward, as among birds. At the two lower corners of the sec- 

 tion of the cerebrum are two distinct rounded cerebral masses 

 which extend outward beyond the adjacent part of the cerebrum, 

 so as almost to excavate a way through the region of the alisphe- 

 noid bones (fig. 4, o). The position of these masses below the cere- 

 brum and in the alisphenoids seems to me to demonstrate that they 

 are the optic lobes of the brain ; and since they hold the same posi- 

 tion and proportion as the excavations for the optic lobes of the 

 brain in the skulls of birds, I infer that in this important point the 

 Ornithosaurian brain is identical with the avian brain. To make 

 this clear, I have prepared a vertical section of the cerebral cavity 

 in the skull of an owl in the same relative plane with the section 

 of the fossil skull, and give the figure for comparison (see dia- 

 gram, PI. XI. fig. 5) — from which it will be seen that the only 

 difference between them is, that the owl's brain has a wider cere- 

 brum, and is "marked by lateral cerebral impressions which are 

 not shown in the fossil. These differences are only of the kind 

 which distinguish the brains of difi'erent genera of birds from each 

 other. 



Mr. "Walker's fossil displays the upper surface of the cerebrum 

 (PL XL fig. 2), and, so far as regards the form of the cerebrum, con- 

 firms the evidence from the Woodwardian fossil ; but too little of 

 the under part of the specimen is preserved for it to show the optic 

 lobes. The cerebral lobes are jf of an inch long, and each is -^ of 

 an inch wide ; they have the lateral outline rounded, and the front 

 outlines combined in the middle to make the front of the brain 

 rounded. The lateral outlines similarly converge behind, except 

 that in between the hinder mesial part of the cerebral hemi- 

 spheres is placed a distinct, small, convex, cerebral mass (PI. XI. 

 fig. 2, e m). It is separated from the cerebral lobes by well-marked 

 grooves directed backward and outward, and does not extend be- 

 tween them for more than jL. inch. In a line with the hinder 

 limit of the cerebral lobes this mass attains its greatest width 

 of about -j^ inch ; and behind this line the cerebral mass be- 

 comes a little narrower. The outermost corners of this mass 

 are each prolonged as a slightly elevated ridge obliquely out- 



