42 



BULLETIN 89, UNITED STATES NATIONAL MUSEUM. 



Triceratops, as identified by Hay, 1 and, as he observes, "probably transmitted a 



vein. 



Anterior to the foramina just described are. two larger openings shown in 

 figure 10, IX, XI. In specimen No. 2274, from which the drawing was made, 

 these foramina appear to be separated externally by a thin bony partition, but in 

 specimen No. 6645 they are confluent, forming one large opening into the brain case. 

 From the location of these openings when compared with those, of other reptilian 

 skulls, I would identify the anterior one as the fenestra ovalis (fig. 10, VIII) and the 

 posterior one as the foramen lacerum posterius or juglar foramen (fig. 10, IX, XI) 

 through which the pneumogastric, vagus, and glossopharyngeal nerves were trans- 

 mitted. Whether these foramina enter the brain case by distinct openings, or 



as.fif celsfh ' 



a.sfto 

 a.nrf 



o. 



-poc 



ji?i>o 



Fig. 10. — Oblique siue view of the posterior part of tee skull ok Stegosaurus sp. Cat. 

 no. 2274, U.S.N.M. J Nat. size, alsp, Alisphenoid; a.pf, articular border for postor- 

 dital; a.prf, articular border for prefrontal; a.spo, articular border for post- 

 frontal; bo, basiocctpital; bs, basisphenoid; c, exit for carotid artery; no, exoccipital; 

 /, frontal; o, orbit; oc, occipital condyle; orsp, orbitosphexoid; p, parietal; poc, 

 PA A occipital process; ppc, process for pterygoid; pro, prootic; psp, presphenoid; 

 sq, squamosal; V, VII, VIII, /AT, AT, XI, and XII, exits of cranial nerves. 



as in Triceratops and Camptosaurus by a single foramen can not be definitely 

 determined from the available specimens. 



In figure 10 the foramen labeled '"VII" is the exit of the seventh or facial nerve. 

 It has the same position as in Triceratops, Camptosaurus, and the alligator, and as 

 in those animals, passes straight through the center of the prootic bone. 



The position of the next foramen forward of the seventh, i. e., in front of the 

 prootic and behind the center of the alisphenoid, at once distinguishes it as the 

 foramen ovale, through which the third division of the trigeminal nerve always 

 leaves the skull (V, fig. 10). As in Camptosaurus, this opening is largely within the 

 prootic, only the anterior boundary being formed by a descending process of the 

 alisphenoid. Immediately below the foramen ovale is a deep, almost vertical fissure 

 on the side of the basisphenoid and from which a short foramen leads into the 



' rroc. TJ. S. Nat. Mus., toI. 36, 1909, p. 100, pi. 2, figs. 1 and 2, a cf. 



