De ATLAS CHAP. 
atlas, and articulates with the skull. .The most remarkable 
fact about this bone (shared, however, by lower Vertebrates) 
is that its centrum is detached from it and attached to the 
next vertebra, in connexion with which it will be referred 
Za 
Fic. 7.—Human atlas (young), showing de- Fic. 8.—Inferior surface of atlas of 
velopment. x}. as, Articular surface for Dog. x4. sn, Foramen for first 
occiput ; g, groove for first spinal nerve spinal nerve; v, vertebrarterial 
and vertebral artery ; 7, inferior arch ; canal. (From Flower’s Osteoloqy.) 
t, transverse process. (From Flower’s 
Osteoloqy.) 
to immediately. The whole bone thus gets a ring-like form, 
and the salient processes of other vertebrae are but little de- 
, veloped, with the exception of 
the transverse processes, which 
are wide and wing-like. In 
many Marsupials, such as_ the 
Wombat and Kangaroo, the arch 
of the atlas is open below, there 
Fic. 9.—Atlas of Kangaroo. .. . (From being no centre of ossification. 
Parker and Haswell’s Zoology.) 
In others, such as Thylacinus, 
there is a distinct nodule of bone in this situation not con- 
crescent with the rest of the arch. 
The second vertebra, which is known as the axis or epi- 
stropheus, is a compound structure, the anterior “ odontoid process,” 
which fits into the ring of the atlas, being in reality the 
detached centrum of that vertebra.’ It is a curious fact about 
that process that it has independently become spoon-shaped in 
two divisions of Ungulates; that it has become so seems to be 
shown by the fact that in the earlier types of both it has the 
simple peg-like form, which is the prevailing form. The cervical 
' Its independence from the epistropheus is emphasised in Monotremes and 
some Marsupials by its late fusion with that vertebra. 
