86 0. 0. Marsh — The Skull and Brain of (Jlaosawrus. 



The Bral,,. 



The brain of Claosaurus was very small, its size in propor- 

 tion to the skull being represented in Plate V, figure 5, which 

 also shows the exact position of the brain in the cranium. A 

 cast of the brain-cavity is shown in the same plate, figure -i, 

 one-fourth natural size. The brain as a whole was consider- 

 ably elongated, especially the posterior half. The olfactory 

 lobes were well developed, and not separated by an osseous 

 septum. The cerebral hemispheres were comparatively large, 

 forming nearly or quite half of the whole brain. The optic 

 lobes were narrow, but considerably elevated. The cerebellum 

 was rather small, and also much compressed. The medulla 

 was of good size, and nearly circular in transverse out- 

 line. The pituitary body was quite large. The interpretation 

 of some of the more minute features of the brain is a matter of 

 difficulty, and will be more fully discussed elsewhere. 



The specimens here described were obtained by Mr. J. B. 

 Hatcher and Mr. A. L. Sullins, in the Ceratops beds of the 

 Laramie, in Wyoming. In the same horizon were found other 

 herbivorous Dinosaurs, especially the gigantic Oeratopsidce, 

 and with them various small Cretaceous mammals. 

 New Haven, Conn.. Dec. 14th, 1892. 



EXPLANATION OF PLATES. 



Plate IV. 



Figure 1. — Skull of Claosaurus annectens, Marsh ; seen from the left. 

 Figure 2. — The same skull ; front view. 

 Figure 3. — The same skull; seen from above. 



All the figures are one-tenth natural size. 



Plate V. 



Figure 1. — Series of five lower teeth of Claosaurus annectens : inner view. 

 Figure 2. — The same teeth ; side view. 

 Figure 3. — The same teeth ; outer view. 



The figures are one-half natural size. 

 Figure 4. — Brain cast of Claosaurus annectens: side view: one-fourth natural 

 size. 

 c, cerebral hemispheres ; ci, cerebellum : m, medulla ; ol. olfactory lobe ; 

 on, optic nerve: op. optic lobe ; p, pituitary body. 

 Figure 5. — -Skull of Claosaurus annectens, with brain cast: top view ; one-tenth 

 natural size. 

 a, nasal opening ; b, orbit ; c, infra-temporal fossa ; cl. dentary ; e. 

 exoccipital ; /, frontal : fp. postfrontal ; j, jugal ; I, lachrymal ; m, 

 maxillary: n, nasal: pf, prefrontal; pm, premaxillary; q. quadrate; 

 qj, quadrato-jugal ; s, squamosal . 



