160 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxxii. 



slightl}' cupped and but little roughened, and in this specimen at 

 least, shows no indication of coalescence with the axis. The anterior 

 surface is rounded, not evenly, but somewhat constricted a))out the 

 middle. The upper surface, which forms the tloor of the neural 

 canal, is slightly concave transversely. 



Measureinenti^ of atlas. 



mm. 



No. 5384. (xreatest lengtli nt interceiitrum 15 



No.. 5384. Greatest Avidth of intercentruni '. . . 34 



No. 5384. Greatest height of atlas 55 



Axis. — The centrum of the axis is opisthoccchis and especialh' light 

 and delicate in its construction. With certain modifications the cen- 



trimi is concave longi- 

 tudinally both on its lat- 

 eral and central surfaces 

 and convex transversely. 

 The greatest length of the 

 centrum is a trifle more 

 than two-thirds the height 

 ys^ of the vertebra from the 

 ventral siu'face to the top 

 of the neural spine. In 

 ^^^^^^BiH» ---B^msB these dimensions it difters 



from the axis of JL 

 grandis, whose length of 

 centrum is hardly more 

 than one-half the height 

 of the vertebra. (See fig. 



6.) • 



^K^^SSi^^^V-^ H M > I » l> ^'^ ^^^® ^^^^ ^^^® ^"^ ^ 



deep pleurocentral cav- 



Fiti. 6.— Side view of axis and part of atlas of Morosau- [^y ^\yq depth of which is 



KUS GRANDIS (NO. 1905 YaLE UNIVERSITY MUSEUM), ABOUT .'ill. -1 . f 



^ NAT. SIZE. a, LEFT HALF OF NEURAL ARCH OF ATLAS; b, prOOaOly SOUICW Uat CX- 



possible intercentrum of AXIS; o, ODONTOID PROCESS; ao'K'crated bv crushiny'. 



p. S?/a, POSTERIOR ZYGAPOPHYSIS. r^^. • , '• j i 



ihis cavity is separated 

 from the very shallow one of the opposite side by a thin septum of 

 bone. Posteriorly this cavity is only separated from the cup for 

 the ball of the succeeding vertebra l)y a thin convex plate of bone. 

 Anteriorly it ends a little in advance of the center of the centrum. 

 The anterior end of the centrum is gently rounded on either side. A 

 vertical plate is developed behind, which is a cu])like excavation and 

 lies in front of the pleurocentral cavity. On either side of the ante- 

 rior ventral surface are what might )>o called infralatoral cavities. 

 These extend well forward into the ball of the centrum and are sepa- 

 rated from one another by a tliln nu^diait })lat(' of hone. These cavi- 



