ARTICULATIONS OF THE ATLAS, AXIS, AND OCCIPITAL BONE. 157 



directly upwards from the summit of the odontoid process to the centre of the 

 anterior margin of the foramen magnum. 



The central odontoid ligament is developed around the notochord in the interval between 

 the basioccipital and first vertebral centrum, and may therefore be said to represent an inter- 

 vertebral disc. The transverse ligament of the atlas and the lateral odontoid ligaments are 

 derived from ligamenta conjugalia costarum (p. 159). 



The posterior occipito-axial ligament is a strong wide band, covering the 

 cruciform and odontoid ligaments. It is attached above in the basilarjjroove of the 

 occipital bone, and below to the body of the axis ; many of the superficial fibres are 

 prolonged into the posterior common ligament, of which it forms the continuation 

 upwards. 



The anterior occipito-atlantal ligament extends from the anterior border 

 of the occipital foramen, between the condyles, to the anterior arch of the* atlas. 



Fig. 183. THE LIGAMENTOUS STRUCTURES WHICH SURROUND THE ARTICULATIONS OF THE OCCIPUT 



AND TWO UPPER VERTEBRAE. A 



A, the lower part of the skull sawn transversely through the basilar process, with the atlas and axis, 

 viewed from before. 1, anterior occipito-atlantal ligament ; 2, accessory occipito-atlantal ligament ; 3, 

 anterior atlanto-axial ligament. 



B, the lower part of the skull, with three adjacent vertebrae, viewed from behind. 1, posterior 

 occipito-atlantal ligament ; 2, posterior atlanto-axial ligament. 



0, the occipital bone sawn transversely through the foramen magnum, and a part of the arches o 

 the atlas and axis removed, so as to show the posterior occipito-axial ligament. 



It is thin and membranous ; but in the median line it is strengthened by an acces- 

 sory ligament, thick and round, placed in front of it, which is sometimes described 

 as the commencement of the anterior common ligament. 



The anterior atlanto-axial ligament, likewise thin and membranous, except 

 in the middle, where it is similarly thickened by a prolongation of the anterior 

 common ligament, extends from the anterior arch of the atlas to the body of the 

 axis. 



The posterior occipito-atlantal ligament, thin and membranous, is attached 

 superiorly to the margin of the occipital foramen behind the condyles, and inferiorly 



