NO. 1519. MOROSA UR US A GILIS REDESCRIBED^GILMORE. 159 



occipital condyle. Posteriorly it articulates with the odontoid and 

 intercentrum of the axis. The median superior surface is concave 

 transversely and somewhat convex antero-posteriorly. On either side 

 of this median concave portion are l)road articular surfaces upon which 

 the pedicels of the neural arch rest. The somewhat roug'hened surfaces 

 of these facets look upward and slightly outward instead of upward and 

 outward, as Doctor Holland" has shown to be the case on the inter- 

 centrum of Diplodoeus. The ventral surface is slightly concave antero- 

 posteriorly and quite evenly rounded transversely'. On either side of 

 the median line of the posterior margin of the lower surface are small 

 facets (see fig. 5 and also JPlate XII/. ), which represent the points of 

 attachment for the cervical ribs. Just above these processes on the 

 lateral surfaces the bone is somewhat excavated, foi'ming two shallow 

 pits. 



The neural arch, or neurocentrum, is an irregularly curved bone, 

 strongly concave inwardly and convex outwardly. It articulates^ with 

 the intercentrum by means of a heav}^ articular 

 base from which rises a broad, winglike plate. 

 This articular end has three faces, one which 

 unites with the intercentrum, a second large one 

 which looks forward and inward and forms a part 

 of the cup for the reception of the occipital con- 

 dyle, and a third, the smallest of the three, which 

 looks backward and inward and opposes the lateral 

 anterior face of the odontoid. These faces all meet fig. .v-antekior view 



,, J 1 i 1 * 1 ii j_' 1 OF ATL.\.S OF MOROSAU- 



one another at obtuse angles. Above the articular j^^^.^ ^^jlis (Cat. no. 

 end just described the shaft of the neural arch is 5384), ix at. size. a. in, 



,..,,. . ..I- I'j. • V . INTERCENTRUM OF AT- 



constricted, but superior to this neck it widens out j^g. ^^ neural arch: 

 into a broad, thin, curved plate which, with the o, odontoid; r, rib fa- 

 plate of the opposite arch, forms the covering 

 of the neural canal. Where these plates oppose one another supe- 

 riorly the ends are broadly rounded antero-posteriorly, though prob- 

 abl}' they never united, but were held together by ligamentary 

 attachments. This plate, where it broadens anteriorly, terminates 

 evenly in a thin, sharp, vertical edge, which is overlapped by the pos- 

 terior extension of the pro-atlas. The posterior extent of the neuro- 

 centrum can not' be determined accurately from this specimen, 

 although the presence of anterior zygapophyses on the axis (see Plates 

 XII and Xllla. zyg.) would indicate that the 'process continued far 

 enough posteriorly to articulate with this surface.'^ Marsh's figure of 

 the posterior view of the skull is apparently defective in this respect. 

 (See fig. 1.) The odontoid or ■pleurocentrum has sufi'ered considerably 

 from crushing, but enough is preserved to determine its most im- 

 portant characters. The posterior articular face (see fig. \c\) is 



«W. J. Holland, Memoirs of Carnegie Miis., Pittsburg, II, No. (1, p. 247 

 ''The posterior extension ot this element in J/, grandis is well shown in rig. (>. 



