AETICULATIONS OF TEE HEAD. 



137 



2. Occipito-atloid Articulation. 



(^Preparation.— 'Diaaect away all the soft parts that pass from the neck to the head 

 and cover the articulation, and more particularly the ilexor, 

 the recti, and the small oblique muscles of the head. To yW 81 



expose the synovial membranes, open the sides of the capsular "' ' 



■ ligament.) 



This is a condyloid articulation. 



Articular surfaces. — In the atlas, the two cavities 

 whict replace the anterior articular processes and 

 the heads of the other vertebrte ; in the occipital 

 bone, the two condyles flanking the sides of the occi- 

 pital foramen. 



Mode of union. — A single capsular ligament en- 

 velopes the entire articulation ; it is attached by its 

 anterior border to the margin of the occipital con- 

 dyles, and by its posterior to the anterior contour of the 

 atlas. Thin and slightly elastic in its inferior half, 

 this ligament presents, superiorly, four reinforcing 

 fasciculi : two middle, which intercross in X — from 

 whence the name " cruciform," sometimes given to this 

 ligament (Fig. 81, 1, 1) ; and two lateral, which pass 

 from the sides of the atlas to the base of the styloid 

 processes (Fig. 81, 2, 2). It is lined within by the 

 synovial membranes, and is enveloped externally by a 

 large number of muscles, which protect the articu- 

 lation and greatly strengthen it everywhere. Among 

 these may be particularly noticed the straight muscles 

 of the head, the small oblique, and the great com- 

 plexus. There is also the cord of the cervical liga- 

 ment. 



Synovial membranes. — These membranes are two 

 in number, one for each condyle and corresponding 

 ctloid cavity. Sustained above, below, and outwardly 

 by the capsular ligament, they are related inwardly 

 to the dura mater and to the fibrous tractus which, 

 from the odontoid ligament, is carried to the in- 

 ternal face of the occipital condyles. 



Movements. — Extension, flexion, lateral inclination, 

 and circumduction, are the possible movements of the 

 occipito-atloid articulation. 



In the Pig, Bog, and Gat this articulation, strengthened 

 as it is by the capsular and odontoido-occipital ligaments 

 already mentioned, has only one synovial capsule. 



3. Articulations of the Bones of the Head. 



If we except the articulation which unites the 

 inferior jaw to the cranium — the temporo-maxillary — 

 and the hyoideal articulations, it will be found that 

 all the bones of the cranium and face are united to 

 each other by synarthrosis, forming the different 

 kinds of sutures already generally described (page 128). 

 Nothing is to be gained by entering into more detail 



ATLO-OXOID AND OCCIPI- 

 TO-ATLOID ARTICULA- 

 TIONS. The upper arch 

 of the atlas has been 

 removed to show the 

 odontoid ligament. 



1, 1, Middle accessory fas- 

 ciculi ; 2, 2, Lateral 

 fasciculi of the capsular 

 ligament of the occipito- 

 atloid articulation ; 3, 

 Odontoid ligament ; 4, 

 Interspinous ligament 

 uniting the second and 

 third vertebras of the 

 neck ; 5, Fibrous capsule 

 uniting the articular 

 processes of these verte- 

 brae. — A, Anterior in- 

 ternal foramen of the 

 atlas converted into a 

 groove by the section of 

 the bone ; B, a. Verte- 

 bral foramina of the 

 atlas ; c, 0, Foramina 

 replacing the anterior 

 notches of the axis. 



