0 WILLIAM K. GREGORY 
Bm | \\ 
Z 
Ve 
No. 5117 A.M. 
Fig. 9 Brain case of a theropod dinosaur, Tyrannosaurus rex (Osborn, Mem. 
Am. Mus. Nat. Hist., n.s., vol. i, pt.i., text fig. 8, p.15). Fullfront view. Deter- 
mination of foramina by Mr. Barnum Brown and by the present writer with the 
kind assistance of Dr. F. von Huene. 
The alisphenoid (marked O.sp. ) lies behind the foramen for nerves II, ITI, in front of the prootic for- 
amen (V) and carotid canal. The lateral wing marked ?P.sp. may represent the true orbitosphenoid, 
which is continuous below with the presphenoid. 
in crocodiles and Dinosaurs they are continuous with the | 
presphenoid. 
There can be little doubt then, that the mammalian alisphe- 
noids have been derived from ‘alisphenoids’ of the type repre- 
