142 LIGAMENTS OF THE LOWER JAW. 



The posterior ligament is a thin and membranous layer, passing be- 

 tween the posterior arch of the atlas and the laminae of the axis. 



The capsular ligaments surround the articular processes of the atlas and 

 axis ; they are loose, to permit of the freedom of movement which sub- 

 sists between these vertebrae. The ligamentous fibres are most numerous 

 on the outer and anterior part of the articulation, arid the synovial mem- 

 brane usually communicates with the synovial cavity between the trans- 

 verse ligament and the odontoid process. 



The transverse ligament is a strong ligamentous band, which arches 

 across the area of the ring of the atlas from a rough tubercle upon the 



inner surface of one articular process to a 

 Flg * 78< * similar tubercle on the other. It serves 



to retain the odontoid process of the axis, 

 in connexion with the anterior arch of the 

 atlas. As it crosses the odontoid process, 

 some fibres are sent downwards to be at- 

 tached to the body of the axis, and others 

 pass upwards to be inserted into the basi- 

 lar process of the occipital bone ; hence 

 the ligament has a cross-like appearance, 

 derived from these appendices, and has 

 been denominated cruciform. A synovial 



membrane is situated between the transverse ligament and the odontoid 

 process ; and another between that process and the inner surface of the 

 anterior arch of the atlas. 



Actions. It is the peculiar disposition of this ligament in relation to 

 the odontoid process, that enables the atlas, and with it the entire cra- 

 nium, to rotate upon the axis ; the perfect freedom of movement between 

 these bones being insured by the two synovial membranes. The lower 

 part of the ring, formed by the transverse ligament with the atlas, is 

 smaller than the upper, while the summit of the odontoid process is larger 

 than its base ; so that the process is still retained in its position by the 

 transverse ligament, when the other ligaments are cut through. The ex- 

 tent to which the rotation of the head upon the axis can be carried is de- 

 termined by the odontoid ligaments. The odontoid process with its liga- 

 ments is covered in by the occipito-axoid ligament. 



5. Articulation of the lower jaw. The lower jaw has properly but one 

 ligament, the external lateral ; the ligaments usually described are three 

 in number ; to which may be added, as appertaining to the mechanism 

 of the joint, an interarticular fibrous cartilage, and two synovial mem 

 branes, 



External lateral, Interarticular fibrous-cartilage, 



Internal lateral, Two synovial membranes, 



Capsular. 



* A posterior view of the ligaments connecting the atlas, the axis, and the occipital 

 bone. The posterior part of the occipital bone has been sawn away, and the arches 

 of the atlas and axis removed. 1. The superior part of the occipito-axoid ligament, 

 which has been cut away in order to show the ligaments beneath. 2. The transverse 

 ligament of the atlas. 3. 4. The ascending and dc.-ccnding slips of the transverse liga- 

 ment, which have obtained for it the title of cruciform ligament. 5. One of the odon- 

 toid ligaments; the fellow ligament is seen on thr opposite side. G. One of the ooci- 

 pi:o-atioid capsular ligaments. 7. One of the atlo-axoid capsular ligaments. 



