214 
THE 
ARTICULATIONS OF THE HORSE 
vaded by the process of ossification early, so that the consolidation of the sacrum 
is usually complete, or nearly so, at three years. 
The coccygeal vertebrie are united by relatively thick intervertebral fibro-cartil- 
ages, which have the form of biconcave dises. 
there is a continuous sheath of fibrous tissue. 
In old horses the first coccygeal vertebra is often fused with the 
sive and varied. 
sacrum. 
Special ligaments are not present, but 
The movement in this region is exten- 
MOVEMENTS OF THE VERTEBRAL COLUMN 
The movements of the spine, exclusive of those at the atlanto-axial joint, are 
dorsal, ventral, and lateral flexion, and rotation. 
929 
232. 
—ATLANTO-OCCIPITAL AND 
ATLANTO- AXIAL JOINTS 
Horse; DorsaL VIEW AFTER 
Remova. or DorsaL ARCH OF 
Fic. 
OF 
ATLAS. 
a, Joint capsule of left part of 
atlanto-oecipital joint; 6, lateral 
ligament of same; c, c’, igament of 
the dens; d, atlanto-axial joint cap- 
sule; e, joint capsule of articulation 
and third cervical 
between axis 
vertebra; /, interspinous ligament; 
1, occipital bone; 2, atlas; 3, axis; 
4, third cervical vertebra; 5, dorsal 
longitudinal ligament.  (Ellenber- 
ger-Baum, Anat. d. Haustiere.) 
THE ATLANTO-OCCIPITAL ARTICULATION 
This joint may be classed as a ginglymus. 
joint are: (1) On the atlas, two deep oval cavities; (2) the corresponding condyles 
of the occipital bone. 
The range of movement at a 
single joint is small, but the sum of the movements is 
considerable. The movements are freest in the cervical 
and coecygeal regions. Rotation is extremely limited 
in the thoracic and lumbar regions. 
ATLANTO-AXIAL ARTICULATION 
This is a trochoid or pivot joint of a rather peculiar 
character. The articular surfaces are: (1) On the lateral 
masses of the atlas, two somewhat saddle-shaped facets, 
which are separated by a wide notch above and a narrow 
one below; (2) on the axis, reciprocal saddle-shaped sur- 
faces which extend upon the dens and are confluent on 
its ventral aspect. It will be observed that the joint 
surfaces are not at all accurately adapted to each other, 
so that only limited areas are in contact at any time. 
The joint capsule is attached around the margins 
of the articular surfaces. It is loose and ample enough 
laterally to allow extensive movement. 
The dorsal atlanto-axial ligament (Lig. interar- 
cuale) is membranous and reinforces the capsule dor- 
sally. 
The interspinous ligament (Lig. interspinale) con- 
sists of two elastic bands which extend from the dorsal 
arch of the atlas to the spine of the axis. 
The ventral atlanto-axial ligament (Lig. dentis ex- 
ternum) arises from the ventral tubercle of the atlas and 
is attached by two branches on the ventral spine of the 
axis. 
The ligament of the dens or odontoid ligament (Lig. 
dentis internum) is short, very strong, and somewhat fan- 
shaped. It extends from the rough concave dorsal sur- 
face of the dens, widens in front, and is attached to the 
transverse rough area on the inner surface of the ventral 
arch of the atlas. 
Movements.—The atlas and the head rotate upon | 
the axis; the axis of rotation passes through the center 
of the body of the axis. 
The articular surfaces of this | 
