NO. 1666. 



OSTEOLOGY OF CAMPTOSAVRUS—OILMORE. 



207 



transversely and forms the floor of the foramen magnum. On either 

 side of this depression are rough siitiiral surfaces for the exoccipitals, 

 the posterior terminations of which enter slightly into the formation 

 of the ball of the occijiital condyle at its upper lateral corners. 



Exoccipital and opistJiotlc or paraoccipital. — The exoccipitals form 

 the greater j)art of the boundary of the foramen magnum and con- 

 tribute' slightly to the formation of the occipital condyle. Seen from 

 behind, they rise as pillars from the condyle, articulating dorsally by 

 oblique sutures AA-ith the supra-occipital, and continuing latero- 

 posteriorly into the broad opisthotics or paraoccipitals. On the 

 median posterior surface, just external to the lateral border of the 

 foramen magnum, are pronounced circular depressions (see fig. 4). 

 Dorsally, the paraoccipital appears to support the parieto-squamosal 

 processes much as in Stegosaurxs. The exoccipital and opisthotic are 

 firmly coalesced, and there 

 is no indication of the 

 position of the suture, 

 which evidently was early 

 obliterated. On the in- 

 ferior lateral surface of 

 the exoccipital are four 

 small foramina, one in 

 front of another, the an- 

 terior one being separated 

 from the other three by an 

 oblique ridge. The more 

 jDosterior pierces the ex- 

 occipital and enters the 

 foramen magnum just 

 within the external open- 

 ing of the latter. As in 

 Morosaurvs agilis^ Diplodocus^ Sfef/osaurus, and Ti'ieeratops^ this 

 doubtless served to transmit the hypoglossal, or twelfth nerve; 

 the next anterior which enters the foramen more inferiorly, instead 

 of a branch of the twelfth nerve, as indicated in the figures, may 

 have transmitted a vein, as in the crocodile; the third, which is 

 separated from those posteriorly by a slight vertical ridge, was 

 probably the exit for the pneumogastric and glossopharyngial nerves, 

 while the fourth, the function of wdiich is undetermined, passes 

 diagonally through the outer anterior edge of the exoccipital and 

 enters the large foramen just within its external opening. The 

 nearly vertical suture between the opisthotic and prootic is plainly 

 indicated on the portion of the skidl of Cat. No. 5473, U.S.N.M. (see 

 fig. 5). The broad paraoccipital processes extend outward and 

 backward beyond the posterior termination of the condyle (see Plate 

 10, fig. 2). Viewed posteriorly (see fig. 4), the median part is con- 



al. sp 

 ix,x 

 bs 



Pig. 4. — Posteriou view of occirnwL kegion of 



SKULL of CAMPT0.SAURUS DISPAR MaBSH. CaT. No. 

 5473, U.S.N.M. : g NAT. SIZE. Al. sp., ALISPHE- 

 NOID ; hS, BASISPHENOID ;• eXO, EXOCCIPITAL ; fm, 

 foramen MAGNUM ; OC, OCCIPITAL CONDYLE ; J)OC, 

 PARAOCCIPITAL PROCESS OR OPISTHOTIC ; p. pt, 

 PROCESS ON BASISPHENOID WHICH MEETS THE 

 PTERYGOID ; SO, SUPRAOCCIPITAL ; IX, X, FORA- 

 MEN LACERUM POSTERH'S. 



