22 



TBE BONES. 



great development of its transversal diameter, the considerable dimensions 

 of the spinal foramen, and the thinness of its body. The intra-rsfejiiflian- 

 face of the latter is divided into two portions by a transverse ridge : one 

 anterior, furnished with ligamentous imprints, exhibits, laterally, two deep 

 excavations, which lodge the venous sinuses ; the other, posterior, is smooth 

 and concave from side to side, and forms an articular surface into which 

 is received the odontoid process of the axis; this surface resembles the 



cotyloid cavity. The inferior spine of the 

 body appears as a large tubercle. The head 

 is absent, and is replaced by two concave 

 facets. The anterior articular processes have 

 their gliding surfaces looking downwards; 

 they are joined to the two preceding facets 

 to constitute two large diarthrodial cavities, 

 which correspond to the occipital condyles. 

 There is no spinous process, but a rough- 

 ened surface instead. The transverse pro- 

 cesses are large, flattened above and below, 

 incline forwards and downwards, and are 

 provided with a thick rugged lip. Pos- 

 teriorly, quite at their base, and on each side 

 of the spinal foramen, they show two large 

 Vertebral or antero-internal fora- vertical facets which represent the posterior 

 "="• 4, Posterior, or cervical fora- articular processes ; these facets are uneven, 



are confounded with the articular cavity of 

 the upper face of the body, and correspond 

 to the two analogous facets of the axis. 

 Each transverse process is pierced at its 

 base by two foramina, which traverse it 

 from below upwards. The posterior repre- 

 sents the vertebral foramen of the other ver- 

 tebras ; while the anterior is continued to the 

 external surface of the process by a wide, 

 deep, but very short channel, running from 

 without to within, and joins a third fora- 

 men, which enters the spinal canal. These 

 last two openings, with the demi-canal 

 which unites them, replace the anterior 

 notch; the posterior is altogether absent. 

 Lastly, an inflected venous canal, whose 

 position varies, and whose presence is not 

 constant, crosses the laminse of the atlas, 

 and opens, on one side, into the spinal 

 canal, and on the other, beneath the trans- 

 verse process. The atlas contains much 

 compact tissue, and is generally developed 

 from SIX centres of ossification : two for the body, which at an early period 

 becomes a solid piece, and two for the annular part ; the other two are 

 complementary centres, each of which forms one of the two posterior 

 undulated facets, and the lip of the corresponding transverse process. 



Second.— This is named the axis (or dentata). It is the longest of all the 

 cervical vertebra ; those which succeed it gradually diminish in length and 

 augment in thickness. The body of the axis has not any head anteriorly, 



atlas; inferior surface. 



, Articular processes for condyles of 



the occipital bone ; 2, ibidem ; 3, 



men; 



-men; 5, Transverse process; 6, 

 Tubercle representing the inferior 

 spinous process; 7, Superior arch, 

 forming the roof of the spinal fora- 

 men. 



A CERVICAL VERTEBRA. 



, Superior spinous process; 2, An- 

 terior articular processes ; 3, " 

 terior articular processes ; 5, An- 

 terior convex face of body; 6, 7, 

 Transverse processes, with their 

 tubercles or rudimentary ribs; 8, 

 Inferior crest, or spine ; 9, Concave 

 posterior face. 



