248 MEMOIRS OF THE CARNEGIE MUSEUM 
wardly and upwardly a process which with the corresponding process of the oppo- 
site arch forms the covering of the upper half of the neural canal. These processes 
do not, either in the specimen before us, or in the specimen figured by Professor 
Marsh, seem to have united to form a neural spine, and they were probably bound 
together by ligamentary attachments. The comparatively short lamina sends back- 
ward a greatly elongated postzygapophysial process, which in its anterior portion is 
excavated on the lower surface, and at its extremity on the lower surface is adapted 
to articulation with the prezygapophyses of the axis. In the specimen figured by 
Professor Marsh this process is represented as broken off, and Professor Marsh’s fig- 
ure, in which an attempt is made to supply the missing portion by a dotted line, 
does not give a correct idea as to its actual length. 
The Odontoid Process (Figs. 16-19). —'The odontoid process was not found with 
the axis described and figured by Mr. Hatcher. He says (Memoirs of the Carnegie 
Museum, Vol. I., p. 20): ‘Only the base of the odontoid process is preserved, but 
this indicates that it was of moderate length with a slightly concave superior sur- 
face.’ A careful examination seems to show that what was preserved of this speci- 
men was the petrified cartilage intervening between the axis and the odontoid, to 
which some fragments of the odontoid were adherent, a partial codssification be- 
tween the odontoid and the axis having taken place. In the specimen preserved 
in the American Museum of Natural History, figures of which are herewith given, 
it is plainly seen that this bone which is morphologically the centrum of the atlas, 
existed as a separate element of the cervix, as is always the case in the Chelonians, 
and exceptionally in the mammalia, even including man. The bone which is here- 
with figured and described has apparently sustained some slight injury on its upper 
surface, more particularly on the left hand side. It appears to the writer that a 
piece of the upper surface has been flaked off. The bone shows a distinct fracture, 
Fic. 16. Inferior view of Odontoid. 7.r., rugosities of upper posterior margin ; s., groove between rugosities. 
(One half natural size. ) 
Fic. 17. Superior view of Odontoid. +7.r., posterior rugosities; s., groove through upper surface. (One half 
natural size. ) 
Fic. 18. Posterior view of Odontoid. (One half natural-size. ) 
Fic. 19. Anterior view of Odontoid. (One half natural size. ) 
revealing the internal cellular structure on that side. Otherwise the bone shows 
well-preserved surfaces, and although slightly distorted by pressure, it is not so 
