712 



DISSECTION OF THE NECK. 



process, 

 and two 

 synovial 

 sacs. 



Occipito- 

 atlantal 

 articula- 

 tions are 

 condyloid 

 joints : 



articular 

 surfaces. 



Between 

 atlas and 

 axis are a 

 pivot-joint 

 and two 

 gliding 

 joints : 



articular 

 surfaces of 

 latter. 



Movements 

 of head, 

 kinds of. 



Nodding 

 movement : 

 seat, extent, 

 and checks. 



Inclination 



neck. 



Turning 

 movement 

 between 

 atlas and 



and in neck 



Stern o- 



clavicular 



articulation 



covered surfaces, which correspond to as many synovial sacs. One I 

 surface is on the front of the process, and articulates with the I 

 anterior arch of the atlas ; the other is the floor of the groove I 

 behind the neck of the process, and is in contact with the transverse | 

 ligament. The posterior synovial sac is larger than the anterior. 



OCCIPITO-ATLANTAL ARTICULATIONS. A synovial joint is formed 

 between the condyle of the occipital bone and the upper articular pro- 

 cess of the atlas on each side. Surrounding the articulation is a 

 capsular ligament of scattered fibres, which is strongest externally and I 

 in front. When the joint is opened, the elliptical articular surface of 

 the condyle will be seen to be convex in all directions, and to look 

 outwards as well as downwards. The articular cavity of the atlas 

 has a corresponding direction, upwards and inwards, and is marked by 

 a slight transverse groove, from which the cartilage is often wanting. 



ATLANTO-AXIAL ARTICULATIONS. Three synovial joints exist 

 between the atlas and axis. The central articulation is between the 

 anterior arch of the atlas and the odontoid process, and has already 

 been exposed. The lateral articulations are formed on each side by 

 the inferior articular process of the atlas and the upper articular 

 surface of the axis. These are united by a loose capsule (fig. 251, 4 , 

 p. 708), which is thickened so as to give rise to an accessory ligament 

 at the inner and posterior aspect of the joint. The articular surface 

 of the axis is somewhat convex, and is sloped downwards and 

 outwards ; while that of the atlas presents a slight transverse ridge 

 in the middle, so that the opposed surfaces are more extensively in 

 contact when the atlas is turned to one side, than when it is placed 

 symmetrically over the axis. 



MOVEMENTS OF THE HEAD. The head can be bent forwards 

 flexion, or backwards extension ; it can be inclined towards the 

 shoulder lateral flexion ; and it can be turned to either side 

 rotation. 



Flexion and extension take place in the joints between the atlas 

 and occipital bone ; and the range of movement is greater in the 

 forward than in the backward direction. Flexion is limited mainly 

 by the long occipito-axial and the check ligaments ; extension by the 

 anterior occipito-atlantal ligament, and by the approximation of the 

 occipital bone to the neural arch of the atlas. When the head is 

 moved more freely, flexion and extension of the cervical portion of 

 the spine come into play. 



Lateral flexion is effected mainly by movement between the 

 cervical vertebrae ; but a very slight degree may be due to move- 

 ment having its seat in the occipito-atlantal articulations. 



Rotation takes place in the atlanto-axial articulations, the atlas 

 and head moving together round the pivot formed by the odontoid 

 process. The movement is stopped by the check ligaments. Less 

 than half of the whole possible rotation of the head is obtained 

 between the atlas and axis, the rest being made up in the neck. 



STERNO-CLAVicuLAR ARTICULATION (fig. 256). The articular 

 surfaces of the two bones are not precisely adapted to each other, 



