186 TEE ARTICULATIONS. 



D. Camivora. — The Cat has no cervical ligament, and shows, instead, a raphe like the 

 Pig. In the Dog, the ligament is reduced to a simple cord, continued from the dorso-lumbar 

 ligament, and goes no further than behind the spinous process of the axis. In the Cat, the 

 interspinous ligaments are replaced by small muscular fasciculi ; in the Dog, this substitution 

 only takes place in the xiervical region. The laminae of the first coccygeal vertebrae possess 

 the principal characters which distinguish perfect vertebrae, and are united by vestiges of the 

 articular bands which exist in the other regions of the spine. 



Aeticle IL — Articulations of the Head. 



We will first study the two extrinsic articulations which are the centre of the 

 movements of the head on the spine — the atlo-axoid and occipito-athid articula- 

 tions. Afterwards, we will pass to the examination of the joints which unite the 

 different bones of the head. 



1. Atlo-axoid Articulation (Fig. 124). 



Preparation. — It suffices to remove the soft parts from around the articulation, to expose 

 the interannular, the interspinous, and the inferior odontoid ligament. To examine the superior 

 odontoid ligament and the synovial membrane, one half the atlas and axis must be separated 

 by sawing longitudinally through them from oue side to the other. 



This may be considered as the type of the trochoid articulation. 



Articular surfaces. — To form this articulation, the axis offers its odontoid 

 pivot and the undulated diarthrodial facets at its base. The atlas opposes to the 

 pivot the concave semi-cylindrical surface hollowed on the superior face of its 

 body ; and for the lateral undulated facets it has analogous facets cut on the 

 transverse processes, on each side of the vertebral canal. 



Mode of union. — 1. An odontoid, or odonto-atloid ligament. 2. An inferior 

 atlo-axoid ligament. 3. A superior ditto. 4. A fibrous capsule. 



a. Odontoid ligament (Fig. 124, 3). — Continuous with the common superior 

 vertebral ligament, very short and strong, flattened above and below, and triangu- 

 lar in shape, the odontoid ligament is composed of glistening white fibres, fixed 

 behind in the superior channel of the odontoid process, and inserted in front on 

 the transverse ridge which separates the superior face from the inferior arch of 

 the atlas, as well as on the imprints situated in front of this ridge. It is covered, 

 on its lower face, by the synovial membrane of the articulation ; and its upper 

 surface is in contact with the spinal dura mater. It sends some bands within the 

 condyles of the occipital bone. 



b. Inferior atlo-axoid ligament. — This is a wide, thin, and nacrous-looking 

 band, extending from the inferior face of the axis to the inferior tubercle of the 

 atlas, and is covered by the longus colli muscle ; it is united to the synovial mem- 

 brane by its deep face, and confounded on its bordei-s with the fibrous capsule to 

 be immediately described. It represents the common inferior vertebral ligament. 



c. Superior atlo-axoid ligament. — This exactly represents the interspinous liga- 

 ments of the other cervical articulations. Yellow, elastic, and formed like the 

 two lateral bands, it is continuous, laterally, with the capsular Ugament. It 

 represents the interspinous and interlamellar ligaments. 



d. Capsular ligament. — This, it may be said, is only the interlamellar ligament 

 proper to the atlo-axoid articulation. It commences from the sides of the pre- 

 ceding ligament, and becomes united to the inferior atlo-axoid, after contracting 

 adhesions with the borders of the odontoid Ugament. In this way it encloses the 

 articulation and the spinal canal. Before and beliind, it is attached to the anterior 

 or posterior margin of the bones it unites. Its external face is in contact wiih 



