12 BULLETIN 110, UNITED STATES NATIONAL MUSEUM. 



the posterior view of the skull of Antrodemus as published by Osborn 1 is not ap- 

 parent in the present specimen, the space being filled by the slender outwardly' 

 directed process from the parietal, as shown in figure 4. 



There are deep, vertically elongated depressions lateral to and on either side of 

 the basioccipital and exoccipital bones into which foramina for the IX, XI, and 

 XII cranial nerves make their exit. (See fig. 16, B.) 



Supraoccipital (s. oc). — The supraoccipital in Antrodemus is relatively reduced 

 in size. It is a comparatively narrow, vertical elongated bone that unites by suture 

 with the overhanging parietal, and is not a cartilaginous union as in many of the 

 Predentate dinosaurs. Its lateral borders appear to unite exclusively with the 

 exoccipitals, the latter sending upward narrow, tapering processes that are in- 

 terposed between the parietal and supraoccipital bones. The ventral extent of the 

 supraoccipital can not be determined from this specimen as the sutures around this 

 end have become coalesced and obliterated, but I am inclined to believe that when 

 a specimen is found in which the occipital elements can be entirely differentiated the 

 supraoccipital will be excluded from the superior median boundary of the foramen 

 magnum as it is in the Sauropoda by the median junction of the exoccipitals above 

 that opening as correctly figured by Osborn. On the upper posterior surface a 

 sharp median ridge is developed that joins a similar ridge on the overlaying parietal. , 

 Below the ridge the bone contracts transversely, the median surface being longi- 

 tudinally depressed. On either side of this contracted part of the bone the lateral 

 surface turns abruptly forward and with the exoccipitals forms a vertically elongated 

 depression (fig. 4). Across the upper half the supraoccipital has a transverse width 

 of 38 mm.; below the carina it contracts to 18 mm. in width. 



Alisphenoid (al. sp.). — The alisphenoid in Antrodemus, as in other Theropo- 

 dous dinosaurs, is large when compared with the very much smaller elements in the 

 Predentate and Sauropodous dinosaur skulls. It consists of an inferior and superior 

 branch, the latter turning outward at right angles to the former. Superiorly it unites 

 with the frontal and parietal, posteriorly with the prootics. The outer end of the 

 transverse process is rugosely roughened sub-oval in outline and is received in a pit 

 on the lower side of the postfrontal postorbital complex, a condition that pre- 

 vails in all known dinosaurian crania. The ventral process expands into a thin but 

 broad cimeter-like process, that laps along the sides of the basisphenoid. On 

 the posterior side, at a point about midway between the upper and lower extremi- 

 ties, the bone is notched by the foramen ovale through which the trigeminal or 

 fifth nerve makes its exit from the brain. Internally it joins by lapping suture the 

 orbitosphenoid between which are the exits for the II and III cranial nerves. 

 The upper inner surfaces of the alisphenoids form the walls of that part of the brain 

 case which lodges the cerebral hemispheres. The alisphenoids do not meet the exoc- 

 cipitals, as Osborn 2 has stated they do in Tyrannosaurus , a statement which I 

 think is to be questioned even in that genus. Such a relationship would be most un- 

 usual, and entirely different from any reptile, living or extinct, with which I am 

 acquainted. 



i Mem. Amer. Mus. Nat. Hist., vol. 1, new ser., 1912, pt. 1, fig. 27. 2 Idera., 1912, p. 13. 



