THE BONES OF THE TRUNK 



19 



latter it encroaches very near to the odontoid process. The plane 

 of each is sloped outwards and downwards. The surface is slightly 

 convex from before back- 

 wards and circular, its direc- 

 tion being upwards and out- 

 wards. They articulate with 

 the inferior articular pro- 

 cesses of the atlas, and the 

 movement allowed is rota 

 tion. The inferior articular 

 processes differ from those 

 of most vertebrae only in 

 being situated principally 

 upon the lower borders of 

 the laminae. The superior 

 pair, like all four articular 

 processes of the atlas, 

 being placed in front of 

 the points of exit of the 

 spinal nerves, do not corre- 

 spond in position with the 

 superior articular processes 

 of succeeding vertebrae, but 



Fig. II. — ^The Axis (Superior View). 



occupy a position corresponding with the pedicular portions of 

 the bodies of vertebrae. 



The transverse processes are very short, and are directed out- 

 wards and downwards. Each terminates in a single tubercle. 



The costal processes also terminate in tubercles, and the costo- 

 transverse lamellae are not grooved superiorly. 



The costo-transverse foramen is directed upwards and outwards, 

 the reason of this obliquity being as follows : when the atlas and 

 axis are in position each costo-transverse foramen in the atlas 

 lies farther out than that in the axis. In order, therefore, to 

 obviate any sudden and urdue bend in the vertebral artery, the 

 foramen in the axis is directed obliquely upwards and outwards 

 so as to guide the vertebral artery gradually to the foramen in the 

 atlas. 



There is nothing peculiar about the neural foramen. 



Varieties. — (i) The summit of the odontoid process may present a facet, 

 indicating an articulation with the anterior margin of the foramen magnum of 

 the occipital bone, which in such cases presents a prominence known as the 

 middle occipital condyle. (2) The odontoid process may, in ver>' rare cases, 

 remain separate from the body, thus forming the os dentatum. (3) An 

 odontoid process in two halves has been recorded. 



The seventh cervical vertebra. — ^The distinctive character of this 

 vertebra is the great length of its spinous process, which is the only 

 cervical s^ine that can readily be felt beneath the integiunent of 

 the neck. On account of this outstanding prominence the seventh 

 cervical is known as the vertebra prominens. The spinous process 



