14 THE SKELETON OF THE CAT. 
The Atlas (Fig. 10, 1; Fig. 12).—The first cervical verte- 
bra or atlas has somewhat the form of a seal ring. The 
centrum is absent; it has united with the second vertebra to 
form the odontoid process or dens. Its place is taken in the 
atlas by a narrow flat arch of bone, narrower at the ends than 
in the middle, the ventral arch (Fig. 12, a) of the atlas. This 
connects the lateral, thicker portions of the ring ventrally and 
bears on its caudal margin a blunt tubercle (tuberculum 
anterius, Fig. 12, 4). Laterally the ring is thickened, forming 
thus the lateral masses (c) which are continued into the broad 
thin transverse processes (Fig. 10, g; Fig. 12, d@). Each 
lateral mass bears at its cranial end on its medial surface a 
concave, pear-shaped facet, cranial (or superior) articular facet, 
(Fig. 12, ¢) for articulation with the condyles of the skull. 
These facets look craniomediad. Dorsad of each is a foramen, 
the atlantal foramen (Fig. 10, 7; Fig. 12, g). which pierces 
the dorsal arch at its junction with the lateral mass. Caudal 
to the facet, on the medial face of each lateral mass, within the 
vertebral canal, is a tubercle. To the two tubercles are 
attached the transverse ligament (Fig. 14, 6) which holds in 
place the odontoid process (dens) of the axis. 
That part of the lateral mass which bears the articular facet 
projects craniad of the dorsal arch and is separated by a deep 
triangular notch from the transverse process. Along the 
bottom of this notch runs a groove (Fig. 12, 7), convex 
craniad, which connects the cranial end of the foramen trans- 
versarium and the atlantal foramen. The vertebral artery 
passes along it. The foramen transversarium is circular. It 
is bounded laterally by the lateral masses, and dorsally by the 
dorsal arch. 
The dorsal arch (Fig. 10, #) is two to three times as broad 
as the ventral, has a thick convex cranial border with a median 
notch, and a thin concave caudal border. 
The caudal articular facets (Fig. 12, 4) are borne by the 
caudal ends of the lateral masses. They are slightly concave, 
triangular, and look caudomediad, so that their dorsal borders 
form with the caudal border of the dorsal arch nearly a semi- 
circle. The transverse processes are flat and directed laterad. - 
