128 ARTICULATIONS OF THE TRUNK AND HEAD. 



The occipito-axial ligament, sometimes called apparatus ligamentosus, is 

 placed beneath the upper part of the posterior common ligament, and covers 

 the crucial and odontoid ligaments. It is a broad band attached above in 

 the basilar groove, and below to the body of the axis. 



The anterior occipito-atlantal ligament extends from the anterior border 

 of the occipital foramen, between the condyles, to the margin of the anterior 

 arch of the atlas. It is thin, broad, and membranous ; but in the median 

 line it is strengthened by an accessory 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 thickened, extends from the border of the anterior 

 arch of the atlas to the body of the axis. 



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

 superiorly to all that part of the margin of the occipital foramen which is 

 behind the condyles, and inferiorly to the adjacent border of the arch of 

 the atlas. It is partly blended with the- dura mater. 



The posterior atlanto-axial ligament, similar to the preceding, connects the 

 neural arch of the atlas with that of the axis, in the absence of ligamentum 

 subflavum. 



MOVEMENTS. The atlanto-axial articulation is so constructed that the head, toge- 

 ther with the atlas, is rotated on the axis ; the odontoid process serving as a pivot. The 

 rotation is limited by the check ligaments. The atlanto-occipital articulation takes no 

 part in rotation, but allows the head to be freely raised or depressed upon the vertebral 

 column. When the atlas is placed symmetrically over the axis, it is seen that the 

 opposing articular surfaces, instead of fitting one to the other, come very slightly into 

 contact, the surface of the axis being inclined too little outwards, and presenting an 

 antero-posterior convexity, to which there is no corresponding concavity presented by 

 the atlas ; but a slight rotation brings the bones into a stable position, in which the 

 anterior half of one articular surface of the axis and the posterior half of the other are 

 laid closely against the atlas. It will also be found that a certain amount of oblique 

 motion between the atlas and occipital bone is permitted, by which the anterior half 

 of one condyle and the posterior part of the other may be rested together on the atlas, 

 and that that is the position of greatest stability. This oblique position is that into 

 which the bones are brought when there is any lateral curving of the column, as is 

 the case in the most natural and easy attitudes. 



ARTICULATIONS OF THE RIBS. 



The articulations of the ribs may be divided into three sets, connecting 

 them with the bodies of the vertebrae, with the transverse processes, and 

 with the sternum. 



The costo-mrtebral articulation unites the head of the rib, in most instances, 

 with the bodies of two vertebrae by two distinct synovial joints, supported 

 by ligaments as follows. 



The anterior costo-vertebral , costo- central, or stellate ligament is divided 

 into three bundles, of which the middle one passes horizontally forwards 

 upon the corresponding intervertebral fibro-cartilage, whilst the superior 

 ascends to the body of the vertebra above it, and the inferior descends to 

 that below. In the first, eleventh, and twelfth ribs, this ligament is inserted 

 into only one vertebral body, and into no fibro-cartilage. 



The interarticular ligament is a thin and short band of fibres, which 

 passes transversely from the ridge separating the two articular surfaces on 



