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MEMOIRS OF THE CARNEGIE MUSEUM. 
Catalog No. 1729. 
Under this number has been cataloged an atlas intermediate in size between 
Nos. 1727 and 1728. 
The cervicals in their relative size, in the possession of a deep inferior keel- 
like projection, and in their manner of articulation are decidedly equine in appear- 
ance, though the inferior keel is in most specimens relatively much deeper verti- 
cally than in the horse, and posteriorly widened laterally, giving the posterior 
extremity of the keel a triangular form which is not seen in the horse. The pos- 
terior articular surfaces of the centra of the cervical vertebra from the second to 
the sixth look upward far more strongly than is the case in the horse, or for that 
matter in any other mammal with which the writers are acquainted. The method 
of articulation displayed by the cervical vertebrae shows that the animal was able 
easily to reach the ground with his incisors while in a standing position. 
The Atlas. 
Eleven specimens of the atlas of Moropus were recovered, all of them differing 
EE in size and some of them being better preserved than 
‘ others. The largest specimen, No. 1604, belonging to the 
in mounted skeleton (see Figs. 18-20) has an extreme width, 
measured over the transverse processes, of twenty centi- 
Z meters. The smallest specimen, No. 1726, has an actual 
S width of approximately eleven and a half centimeters, but, 
Fic. 18. Lateralview ofatlas 4. the right transverse process is broken, the true meas- 
of Moropus elatus (No. 1604). on 
So urement in life was not less than twelve and a half centi- 
meters. It evidently belonged to an immature individual. 
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A comparison of the various specimens shows considerable variation in the 
relative width of the upper anterior marginal sinus between the condylar articular 
surfaces. In specimens Nos. 1604, 1728, and 1726, selected for detailed measure- 
ments, this sinus is in each case of nearly the same width, but in specimen 1721, 
which is undoubtedly the atlas of a very immature animal, the sinus is thirty-seven 
millimeters wide, while in most of the other specimens not enumerated here it is 
only about twenty-five millimeters in width. 
The anterior articulating surfaces are widely separated above, but more 
closely approximate each other below, being separated by a notch, which in one 
specimen, No. 1724, is produced downward as a deep narrow cleft. Only vestiges 
of this deep cleft appear in specimens Nos. 17138, 1722, 1727, and 1728, while in 
all others it is wholly obliterated, being solidly filled in with bone. The vertical 
