8 



THE VERTEBRAL COLUMN. 



so as to form a smooth transverse groove the vertebral groove, in which lie the verte- 

 bral artery and first spinal (suboccipital) nerve ; the groove corresponds to the 

 superior notches of the other vertebrae. 



The transverse processes are larger and project farther outwards than those of the 

 subjacent vertebra?. They are flattened from above downwards, and have a large 

 foramen. Their extremities are not bifid, but broad and rough. 



Varieties. The posterior arch of the atlas is sometimes imperfect, the gap in th.e bone 

 being 1 bridged across by a fibrous band. A similar defect in the anterior arch is comparatively 

 rare, but its complete absence has been observed. 1 The transverse process, especially the 

 anterior bar, may also be the seat of defective ossification, and the foramen of the vertebral 

 artery is then completed by ligament. A bony arch over the vertebral groove is frequently met 

 with. Less common is the formation of a canal for the vertebral artery on the outer side of 

 the superior articular process. 



The second vertebra or axis (vert, dentata) forms a pivot on which the 

 first vertebra rotates carrying the head. 



The lody is characterized by the presence of a large blunt tooth-like process called 



F. ARTIC.PROC. 



Fig. 5.- 



-AXIS, FROM THE RIGHT SIDE. 



by D. Gunn.) 



(Drawn 



Fig. 6. SEVENTH CERVICAL VERTEBRA, FROM 

 ABOVE. (Drawn by D. Gunn. ) 



odontoid (proc. dentatus). This consists of an enlarged part termed the head, and a 

 lower part or neck. It has in front a smooth surface for articulation with the 

 atlas, and behind a smooth groove to receive the transverse ligament. The lower 

 surface of the body resembles that of the succeeding vertebrae. Its anterior surface 

 is marked by a low median vertical ridge, with a depression on each side. 



The superior articular surfaces, placed like those of the atlas in front of the notch, 

 lie close to the base of the odontoid process, partly on the body and partly on the 

 pedicles of the vertebra. These surfaces look upwards and slightly outwards. The 

 inferior articular processes are similar in form and position to those of the succeeding 

 vertebrae. 



The spinous process is very large, rough, deeply bifid, and grooved on its inferior 

 surface. The lamina are very thick and strong. 



The transverse processes are short, and the anterior tubercle almost obsolete. The 

 foramen for the vertebral artery is inclined obliquely upwards and outwards. 



The seventh cervical vertebra has a long spinous process, which is not 

 bifurcated, but ends in a broad tubercle projecting under the skin, whence the name 



1 Dwight, Journ. Anat., xxi, 539. 



