i:;<; Tin: M;H< i LAT20N8. 



the .sii|H'iior odontoid ligament and tin -\n<i\ial nn-iiilirani , one half tin- atlas and axis 

 iuu-1 bo MciNiruU.il l>y suwing longitudinally through them from one .-ide to the other.) 



This nmy bo considered as this typo of the trnehoides. 



Artii-nltir mrfafcs. To form this articulation, the axis oilers its odontoid 

 pivot mid the undulatc-d dinrtlirodinl facets at its base. The atlas opposes 

 to the pivot the concave seinieylindneal nurfae" hollowed on the snperi< i 

 face of its body; and for the lateral undulated facets it has analogous i. 

 which arc cut on the transverse processes, on each side of the vertebral eanal. 



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

 inferior atlo-axoid ligament ; 3. A superior ditto ; 4. A fibrous capsul.-. 



a. Odontoid ligament (Fig. 81, 3). Continued to the common superior 

 vertebral ligament, very short and strong, flattened from al>ve to below, 

 .iml triangular in shape, the odontoid ligament is composed of glistening 

 white fibres, fixed behind in the superior channel of the odontoid ju 



and inserted in front on the transverse ridge which separates the; sujM-rior 

 fiiee from the inferior arch of the atlas, as well as on the imprints situated 

 in front of this ridge. This ligament is covered, on its lower face, by the 

 synovial membrane of the articulation ; and by its upper surface is in 

 contact with the spinal dura mnter. It scuds some bauds within the 

 eondyles of the occipital bone. 



b. Inferior atlo-aju.id liyament. 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 covered by the long muscle of the neck ; it is 

 united to the synovial membrane by its deep face, and confounded on its 

 borders with the fibrous capsule to bo immediately described. 



c. Superir/r atlo-axoid ligament. This exactly represents the inter- 

 spinous ligaments of the other cervical articulations. Yellow, elastic, and 

 formed like the two lateral bands, it is continuous, laterally, with the 

 capsular ligament. 



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

 ligament proper to the atlo-axoid articulation. It commences from the 

 sides of the preceding ligament, and becomes united to the inferior atlo- 

 axoid one, after contracting adhesions with the borders of the odontoid 

 ligament. In this way it encloses the articulation and the spinal canal. 

 Jicforo and behind, it is attached to the anterior or posterior margin of 

 the bones it unites. Its external face is in contact with the great oblique 

 muscle. of the head; its internal responds, in its inferior half, to the articular 

 synovial membrane, and its superior moiety to the spinal dura mater. 

 (Lcyh describes this ligament as the interannular.) 



Synovial membrane. This lines the odontoid ligament, the atlo-axoid 

 ligament, and the articular portion of the peripheral capsule. 



Movements. Rotation, the only movement possible in the atlo-axoid 

 articulation, is effected in the following manner: the axis remains fixed, 

 and the first vertebra, drawn to one side chiefly by the great oblique 

 muscle, rotates on the odontoid pivot, carrying the head with it. 



In the Dog and Cat the odontoid ligament is ro]>lu<-l hy tlin < purtimilur ligaments : 

 1, Two lateral canix, rising in common from the Huiiimit <>f tin- odontoid pnvos, and 

 inserted, each on its own side, within the eondyles of tin- oeripiial INHIC ; '2, A //,. 

 Ugvmeai, paaring over the odontoid prooeHL wbioh it maintains in its |>ia. > a-ainst tin- 



inferior arch of tho athis. and is altnchcd l>y its extremities to the Miperior f.i.-r nl' the 

 latter. A Hinull synovial eap.snle facilitate .s the L'lidinic of the odontoid proer.-.-, I., n.alli 

 this ligament. The artifiilar Miiovial meniKraiie alwava couuuuiiicatea \sitli llr.it of the 



ixvipit > -atloid arl ieidal i"H. 



Ill the l',<i the di.s|idoitioi( ia nearly the .-mm; u* in the ( arnivora. 



