ATLAS AND AXIS VEBTEBBJE. 9 



to the rings of the succeeding vertebrae ; the narrower anterior part is occu- 

 pied by the odontoid process of the axis, and in the recent state is separated 



Fig. 6. THE ATLAS VERTEBRA, FRO.M ABOVE. 4 



Fig. 6. 



1, the anterior .arch, with a tubercle in 

 front ; 4, the posterior part of the ring, with 

 5, an indication of a spinous tubercle ; 4', the 

 anterior part of the ring, containing the odon- 

 toid process, and indicatiu.2 in front of 4' the 

 smooth surface on which the process moves 

 in rotation ; 6, the transverse process with a 

 slight indication of division into two tubercles ; 

 7, the condyloid articulating process ; -f inside 

 it indicates the rounded tubercle to which the 

 transverse ligament is attached ; a, the fuiamen 

 in the transverse process ; b, the groove on the 

 posterior arch for the vertebral artery. 



from the posterior by the transverse ligament of the atlas. In front of the 

 ring is the anterior arch, sometimes called the body, from which projects 

 forwards the anterior tubercle, while its posterior aspect presents an arti- 

 cular surface which glides in rotation of the head upon the odontoid process 

 of the axis. At the sides of the ring are the lateral masses two stout 

 portions of bone which receive the weight of the head, and present large 

 articular surfaces on their supeiior and inferior aspects. They are situated 

 in front of the places of exit of the nerves, and in this and other respects 

 differ from the articular processes of the five lower cervical vertebrae. The 

 superior articular surfaces, which receive the condyles of the occipital bone, 

 are of oval form, converging in front, concave from before backwards, and 

 looking inwards as well as upwards. At the internal margin of each is a 

 rounded smooth tubercle with a rough depression, which gives attachment 

 to the transverse ligament. The inferior articular surfaces are smaller than 

 the superior pair, flat, nearly circular, looking downwards and inclined a 

 little inwards. 



Tae laminae unite behind to form a posterior tubercle, the rudiment of a 

 spinous process. They are thick and round in the greater part of their 

 extent, but at their junction with the lateral masses they are flattened 

 by a smooth transverse groove on the upper border of each, marking the 

 course of the vertebral artery as it passes inwards from the foramen of 

 the transverse process before entering the cranium. This groove is some- 

 times converted into a foramen by a small arch of bone. It transmits the 

 suboccipital nerve as well as the vertebral artery, and corresponds with the 

 notches of the other vertebrae. 



The transverse processes project considerably further outwards on each 

 side than those of the vertebrae immediately following ; they are flattened 

 from above downwards and somewhat rough, they are rounded at the ex- 

 tremity, and at the root of each is the foramen which transmits the vertebral 

 artery. 



The SECOND VERTEBRA, Vertebra dentata t or Axis, forms a pivot on which 

 the head with the first vertebra rotates. 



The body is surmounted superiorly by the odontoid process, and is some- 

 what narrowed and prolonged below to fit into the depression of the body 

 of the third vertebra. In front it presents a low vertical ridge, with a 

 depression on each side, to which the upper part of the lougus colli muscle 

 is attached. The odontoid process (p. deutatus) consists of an enlarged 



