176 



THE ARTICULATIONS OF THE HORSE 



movements are freest in the cervical and coccygeal regions, 

 limited in the thoracic and lumbar regions. 



Rotation is extremely 



Fig. 



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 usually 

 confluent ventrally; (2) on the axis, reciprocal saddle- 

 shaped surfaces which extend upon the odontoid pro- 

 cess and are confluent on its ventral aspect. It will be 

 observed that the joint surfaces are not at all accur- 

 ately 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 superior atlanto-axial ligament (Ligamentum 

 interarcuale) is meml:)ranous and reinforces the capsule 

 dorsally. 



The interspinous ligament (Ligamentum inter- 

 spinale) consists of two elastic bands which extend 

 from the dorsal arch of the atlas to the spine of the 

 axis. 



The inferior atlanto-axial ligament (Ligamentum 

 dentis externum) arises from the ventral tubercle of the 

 atlas and is attached by two branches on the ventral 

 spine of the axis. 



The odontoid ligament (Ligamentum dentis in- 

 ternum) is short, very strong, and somewhat fan- 

 shaped. It extends from the rough concave dorsal 

 surface of the dens or odontoid process, 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 odontoid process and body of the axis. 



141. — Atlanto -occipitai, 

 AND Atlanto-axial Joints 

 OF Horse, Dorsal ^'IE^v 

 AFTER Removal of Dor- 

 sal Arch of Atlas. 

 a, Joint capsule of left part 

 of atlanto-occipital joint; b, lat- 

 eral ligament of same; c, c' , odon- 

 toid ligament; d, atlanto-occijjital 

 joint capsule; e, joint capsule of 

 articulation between axis and 

 third cervical vertebra; /, inter- 

 spinous ligament; 1, occii^ital 

 bone; 2, atlas; 3, axis; 4, third 

 cervical vetrebra. (Ellenberger- 

 Baum, Anat. d. Haustiere.) 



THE ATLANTO-OCCIPITAL ARTICULATION 



This joint may l)e classed as a ginglymus. The 

 articular surfaces of this joint are: (1) On the atlas, 

 two deep oval cavities; (2) the corresponding condyles 

 of the occipital ])one. 



The joint surface.s are oblique, coming very close to the 

 median line ventrally, but separated by a considerable interval 

 dorsally. Posteriorly, a triangular rough area cuts into tlie middle of each articular suiface 

 on the atlas. 



There are two roomy joint capsules, whicli sometimes communicate ventrally, 

 especially in old subjects. 



The superior atlanto-occipital membrane extends from the dorsal arch of the 

 atlas to the upper margin of the foramen magnum. It is lilcnded with the capsules 

 and contains many elastic fibers. 



The inferior atlanto-occipital membrane extends from the ventral arch of the 



