Anatomy of Skeleton 



connecting the margins of the articular surfaces ; a corresponding ridge may be visible 



in front. 



The back of the body exhibits two venous foramina with a median ridge, and is 



tuberculated for the attachment of the Membrana tectoria, and accessory alto-axoid 



ligaments : the crus inferior of the cruciate ligament is attached to the transverse line 



and the bone below this. 



The odontoid process articulates in front with the arch of the Atlas and has a 



cartilage-covered facet upon it. Its sides are pierced by small foramina, and its 



posterior surface is grooved by the trans- 

 verse band of the lig. cruciatum : a bursa 

 on cartilage intervenes, which may extend 

 out on the front of the ligament and com- 

 municate with the occipito-atloid joint. 

 The top of the process is divided by a 

 triradiate line into three areas, of which 

 the front is for the median, and the two 

 posterior for the lateral occipito-odontoid 

 ligaments. 



The process, being the separated body of 

 the atlas, is ossified from a bilobed or double 

 centre distinct from that of the true body of the 

 axis, and a plate of cartilage separates the two 

 elements at birth. A few years later the spread- 

 ing ossification involves the peripheral parts of 

 the cartilage, but the central portion remains as 

 cartilage until past middle life. The transverse 

 line mentioned as showing the limits of the pro- 

 cess behind is below the level of the inner part 

 of the articular surface, and many bones indicate 

 on inspection what is suggested by this fact, 

 that the inner corner of the articular surface is 

 ossified from the odontoid centres. Possibly 

 there is an occipital body included in the apex 

 of the proce: s. 



At birth the bone is in four pieces 

 joined by cartilage -the dens, the true 

 body, and the two halves of the neural 

 arch. These are consolidated by the sixth 

 or seventh year. The lines of junction of 

 the neural centres with those of the true 

 body lie below the levels of the pedicles 

 and transverse processes. 



FIG. 21. Schemes to show the modifications of the 

 costal processes in the two upper vertebrae 

 consequent on the adoption of an enlarged 

 neuro-central articulation as a main joint. 



Atlas (Fig. 20). The tip of the anterior tubercle points down, and has the 

 anterior common ligament attached to it : on each side of this (Fig. 19) the Longus 

 colli is inserted on a rough area. The anterior occipito-atloid ligament has a strong 

 median band on the upper part of the tubercle (so that a non-ligamentous area of 

 bone separates this from the lower ligament), and at each side its lateral part makes 

 a ridge on the bone running into the markings of the upper capsule. 



Rectus anticus minor arises from the bone in front of the capsule : this muscle 

 does not as a rule make much definite marking on the bone, but it does not 



