VERTEBRAL COLUMN. 95 



rotation. The confinement of the processus dentatus by the 

 transverse ligament behind, and by the anterior bridge of the 

 first vertebra in front, prevents thoroughly both flexion and ex- 

 tension. The horizontal direction and the flatness of the cor- 

 responding articular faces of these two vertebrae, also prevent 

 any lateral inclination. In compensation for these restrictions, 

 the rotatory motion is enjoyed to great extent, and is amply 

 provided for, by the extreme looseness and thinness of the cap- 

 sular ligament of the oblique processes. In this motion the arch 

 of the atlas and the transverse ligament rotate on the tooth-like 

 process to the right and left alternately; at the same time the 

 inferior oblique process of the atlas is slid either forwards or 

 backwards, according to the general movement upon the upper 

 oblique process of the dentata. This movement is checked, at 

 a certain point, by the moderator ligaments, which, by the close 

 connexion of the head and first vertebra, answer the same pur- 

 pose as if they were inserted into the latter. It is also checked 

 by the capsular ligament, notwithstanding the general laxity of 

 the latter. But still it is not difficult for it to exceed its natu- 

 ral bounds, and for the oblique process of the atlas to pass com- 

 pletely beyond the margin of that of the dentata, and in return- 

 ing to lock against it. This, in fact, happens, in the great majo- 

 rity of instances, where violence from falls, and so on, has been 

 applied to the body, and results in injury to the neck, particularly; 

 and when, in the abrupt turning of the head, produced by the 

 action of the muscles, the individual finds himself incapable of 

 bringing it back. This articulation is, unquestionably, less pro- 

 tected, and more exposed to accident, than any other in the 

 spine; and, as just stated, is therefore supposed, by some, to be 

 the only one in the neck admitting of luxation. 



Most frequently, in this luxation, when it is produced by ex- 

 ternal violence, death is the immediate result, from the spinal 

 marrow being pressed upon and disorganized above the origin 

 of the phrenic nerve. The seat of the principle of respiration 

 is in the medulla oblongata, and its agents are the phrenic and 

 the intercostal nerves; the communication with which being 

 thus cut off, respiration, and consequently circulation, stop im- 

 mediately. Bichat thinks, that, when death is thus suddenly 

 produced, the processus dentatus, by rupturing its own ligaments 

 connecting it to the occiput, slides by the falling of the head 



