THE VERTEBRAL COLUMN. 37 



How are the Vertebrae distinguished? As cervical (7), dorsal (12), anu 

 lumbar (5). Each of these divisions has several peculiar features, but their 

 especial characteristics are as follows. 



The Cervical Vertebra are pierced at the bases of their transverse processes by 

 the vertebral foramina, which transmit the vertebral artery, vein, and plexus. 

 The Dorsal Vertebra have facets and demifacets on their bodies, for articula- 

 tion with the heads of the ribs. 

 The Lumbar Vertebra are marked by the absence of the foramina and facets 



which distinguish the other two classes. 



What are the Peculiar Vertebrae? They are 9 in number, the atlas 

 or 1st cervical, the axis or 2d cervical, the vertebra prominens or 7th cervical, 

 the 1st, 9th, roth, nth, and I2th dorsal, and the 5th lumbar. 



The Atlas is a bony ring supporting the head. A bony arch takes the place 



of a body, and its spinous process is a mere tubercle. Its Lateral Masses 



form its chief bulk, supporting large Articular Processes which all look 



inwards, the superior articulating with the condyles of the occipital bone. 



The Axis is marked by its Odontoid Process projecting upwards from the 



body into the anterior part of the spinal foramen of the atlas, where it 



articulates with the anterior arch, and receives the occipito-axoid and the 



check ligaments. 



The Vertebra Prominens has a long and prominent spinous process which 



ends in a tubercle for the ligamentum nuchae. 



The Dorsal Vertebra. The 1st has one facet and a demifacet. The 9th has 

 a demifacet only. The loth has but one facet on the body and one on 

 the transverse process. The lith and I2th have each but one facet on 

 the body, and none on the transverse processes. The I2th resembles a 

 lumbar vertebra in size and shape. 



The 5th Lumbar is much deeper in front than behind ; its spinous process is 

 small, but its transverse processes are large and thick, and point slightly 

 upwards. 



What important Relations have Certain Vertebrae? 

 The $d Cervical corresponds to the bifurcation of the common carotid artery, 



and the superior cervical ganglion. 



The $th Cervical, to the junctions of the larynx with the trachea, and the phar- 

 ynx with the oesophagus, and the middle cervical ganglion of the sympathetic. 

 The 2d Lttmbar, to the junction of the duodenum with the jejunum, the 

 commencement of the thoracic duct and the portal vein, the origin of 

 the superior mesenteric artery, the lower margin of the pancreas, the 

 opening of the ductus communis choledochus, the lower end of the spinal 

 cord, and the crura of the diaphragm. 

 [The false vertebrae are described as bones of the pelvis.] 

 4 



