LIGAMENTS OP THE LOWER JAW. 125 



some fibres are sent downwards to be attached to the body of the 

 axis, and others pass upwards to be inserted into the basilar pro- 

 cess of the occipital bone ; hence the ligament has a cross-like appear- 

 ance, 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 

 cranium, to rotate upon the axis ; the perfect freedom of movement 

 between these bones being ensured 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 extent to which the rotation of the head upon the 

 axis can be carried is determined by the odontoid ligaments. The 

 odontoid process with its ligaments is covered in by the occipito-axoid 

 ligament. 



5. Articulation of tJie 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 membranes, 



External lateral, 

 Internal lateral, 

 Capsular. 



Interarticular fibrous-cartilage, 



Two synovial membranes. 



Fig. 57.* 



* An external view of the articulation of the lower jaw. 1. The zygomatic 

 arch. 2. The tubercle of the zygoma. 3 The ramus of the lower jaw. 4. The 

 mastoid portion of the temporal bone. 5. The external lateral ligament. 6. The 

 stylo -maxillary ligament. 



