OF THE ATLAS WITH THE AXIS. 191 



most superficial fibres of this ligament connect three or four vertebras; those 

 deeper seated pass between two or three vertebrae ; whilst the deepest connect the 

 contiguous extremities of neighboring vertebrae. 



5. LIGAMENTS CONNECTING THE TRANSVERSE PROCESSES. 

 Inter-transverse. 



The Inter-transverse Ligaments consist of a few thin scattered fibres, interposed 

 between the transverse processes. They are generally wanting in the cervical 

 region; in the dorsal, they are rounded cords; in the lumbar region, thin and 

 membranous. 



Actions. The movements permitted in the spinal column are, Flexion, Exten- 

 sion, Lateral movement, Circumduction, and Eotation. 



In Flexion or movement of the spine forwards, the anterior common ligament 

 is relaxed, and the intervertebral substances are compressed in front; the posterior 

 common ligament, the ligamenta subflava, and the inter-spinous and supra-spinous 

 ligaments are stretched, as well as the posterior fibres of the intervertebral disks. 

 The interspaces between the laminae are widened, and the inferior articular pro- 

 cesses glide upwards, upon the articular processes of the vertebra below. Flexion 

 is the most extensive of all the movements of the spine. 



In Extension or movement of the spine backwards, an exactly opposite dispo- 

 sition of the parts takes place. This movement is not extensive, being limited by 

 the anterior common ligament, and by the approximation of the spinous processes. 



Flexion and extension are most free in the lower part of the lumbar, and in the 

 cervical regions ; extension in the latter region being greater than flexion, the 

 reverse of which exists in the lumbar region. These movements are least free in 

 the middle and upper part of the back. 



In Lateral Movement, the sides of the intervertebral disks are compressed, the 

 extent of motion being limited by the resistance offered by the surrounding liga- 

 ments, and by the approximation of the transverse processes. This movement 

 may take place in any part of the spine, but is most free in the neck and loins. 



Circumduction is very limited, and is produced merely by a succession of the 

 preceding movements. 



Rotation is produced by the twisting of the intervertebral substances; this, 

 although only slight between any two vertebne, produces great extent of move- 

 ment, when it takes place in the whole length of the spine, the front of the column 

 being turned to one or the other side. This movement takes place only to a slight 

 extent in the neck, but is more free in the lower part of the dorsal and lumbar 

 regions. 



It is thus seen, that the cervical region enjoys the greatest extent of each variety 

 of movement, flexion and extension being very free ; lateral movement and rota- 

 tion, although less extensive than the former, being greater than in any other 

 region. In the dorsal region, especially at its upper part, the movements are most 

 limited ; flexion, extension, and lateral motion taking place only to a slight extent, 

 In the lumbar region, all the movements are very free. 



II. ARTICULATION OF THE ATLAS WITH THE AXIS. 



The articulation of the anterior arch of the atlas with the odontoid process forms 

 a lateral ginglymoid joint, whilst that between the articulating processes of the 

 two bones forms a double arthrodia. The ligaments of this articulation are the 



Two Anterior Atlo-axoid. Transverse. 



Posterior Atlo-axoid. Two Capsular. 



Of the Two Anterior Atlo-axoid Ligaments (fig. 117), the most superficial is a 

 rounded cord, situated in the middle line ; attached, above, to the tubercle on the 

 anterior arch of the atlas ; below, to the base of the odontoid process and body of 

 the axis. The deeper ligament is a membranous layer, attached, above, to the 



