HE 
@cipito-axoidien,) is a broad flattened fafciculus, thin at its 
middle, and thicker on the fides. ove it is attached to 
over the 
OW. 
of the atlas with the axis (articulation atiloido-axcidienne). 
Here there are two modes of attachment: the odontoid pro- 
cefs is confined in a peculiar manner, and the body, the 
plates, ad the articular proceffes of the two vertebra are 
joined together. 
The odontvid procefs poffeffes, for its articulation, two 
convex furfaces, an anterior and a polterior, both covered 
by a thin flratum of cartilage. 
a cartilaginous furface. on the back of the anteri 
the atlas ; the latter moves againit the tranfverfe ligament. 
The joint poffeffes two fynovial membranes and a tranfverfe 
odontoid procefs, defcribes in its courfe about the fourth o 
a circle, and thus forms, with the anterior arch of the atlas, 
a kind of ring, in which the odontoid turns, or which turns 
it. It 1s contiguous, behind, to the ligament laft de- 
f the 
axis, and holds the ligament in its proper fituation, The 
upper edge is fometimes furmounted by a {maller tran{verfe 
band, having the fame direétion as the larger one, and fepa- 
t 
rated from it by cellular tiffue. 
anterior fynovial membrane covers the {mooth fur- 
face of the ‘atlas in front, and the anterior one of the odon- 
toid behind. Where it is continued between thefe it is loofe, 
the front of the tranfverfe ligament. It is furrounded 
much cellular fubftance, and allows a free motion of the 
part 
correfponding 
ingui y their 
edge of the front arch of 
' ‘ato the batis. of 
_ The pofterior ligament is. thin-and very loofe, to permit 
the rotatory motions of the atlas on the axis, it arifes from 
ped saga arch of the former, and is inferted into. the 
—— of the latter, Its texture, which is. 
Haag vertebra, ‘I'he recti majores partly cover this liga- 
nt. : = r 
r tually. 
_. The mufcles, pr 
almoit. cellular, 
A D. 
has no analogy to the yellowith ligaments, of which it fille 
the fituation. It correfponds in front to the dura mater, 
behind to the inferior oblique mufcles, and much cellular 
fubftance. 
The fynovial membrane is remarkable for its great laxity, 
which permits a correfponding extent of motion. It covers 
the articular fu and a little of the neighbouring bony 
art of the atlas, then defcends upon the axis, and covers 
its furface. Its loofe portion, continued between thefe two 
parts, is furrounded by much cellular tiffue, on the infide by 
the interior ligaments of the vertebral canal, and externally - 
by the vertebral artery. ‘I'his fynovial membrane is rather 
ftronger than the preceding ones. 
Motions of the Head.—'Vhefe are of two kinds: 1ft, thofe 
in which the head is carried dire€tly forwards, backwards, 
or in any other direétion ; and 2dly, rotation, in which it 
moves on its own axis. 'I'wo feparate articulations are pro- 
vided for thefe movements: the former are effected by the 
joints compofed of the occipital condyles, and the fuperior 
hollows of the atlas; the latter by. the connection of the 
atlas with the axis. 
The motions of the head upon the atlas, are thofe of 
flexion (in which the head is carried towards the front of 
the trunk, or forwards), extenfion (where it is moved in the 
oppolite direétion), and inclination ‘to either fide. In all 
thefe, the cervical region of the vertebral column muft be 
previ fixed to afford a point of fupport. The head 
reprefents in all a lever of the firft kind, in which the 
joint, and the power and refiftance vary” 
The lateral inclination is 
tion jut enumerated ; 
Zi 
a 
the vertebral column, and a confequent relaxation an 
ing of the fkin on the front of the neck, 
trary, when the cervical region of the fpine is. moved for- 
wards, the relation between it and the jaw continues reef 
the fame, and the fkin is, confequently, not affected. 
Moreover, in the former cafe, the head turns on itfelf ; in. 
the latter, where the cervical vertebre communicate their 
motion to the head, a much larger arc of a circle is defcribed. 
b tter. 
: he ligaments, which tie the odontoid. procefs-to the: 
i motion of th d 
occiput, limit the head in.the cavities of the- 
atlas. Luxation cannot roduced in thefé motions ; the. 
articular furfaces are held together too firmly, the motions. 
are too obfcure,.and the odontoid ligaments refift too effec-. 
be divided: 
articulation. 
cing thefe motions, may 
wiz, thofe which affect the 
which are cz to 
lation. Of the fecond 
jaw, and others to the bones of the cranium. 
are: 1, reéti capitis interni minores; 2, recti capitis late. 
rales ;, 3, recti capitis poltici minores;, 4, ¢ ui capitis. 
i cs. 
