922 THE OSTEOLOGY AND MYOLOGY OF THE DEATH ADDER, 



present, but no facets for a zygantrum, the posterior border pro- 

 jecting slightly over the axis, which has no zygosphene. Two 

 small tubercles project from a weakly developed transverse process. 

 The hypapophyseal region consists of a wedge-shaped piece of bone, 

 the anterior portion of the superior surface of which was described 

 above. It articulates with the inferior surface of the basioccipital 

 portion of the condyle of the skull ; it is also in contact with the 

 odontoid process, and with the hypapophysis of the axis. A suture 

 shows its autogenous separation from the atlas upon which it is 

 freely movable. 



The posterior articular surface of the bone presents two concave 

 lateral facets, and a concave inferior fapet. These all articulate 

 with surfaces on the axis. 



The various elements fit on to the occipital condyle in the 

 following manner. The superior portion of the tubercle carries 

 ligaments, while the anterior and inferior part fits into the Y cleft 

 formed by the exoccipitals on either side, and the basioccipital 

 below. The lateral concave wings fit on the exoccipital ; the 

 small convex portion mentioned above fits in between the latter 

 bone and the basioccipital. On the surface of the concave penta- 

 gonal plate of the hypapophysis, the convex surface of the basi- 

 occipital rests ; and since the inferior edge of this bone is produced 

 into a hook-like process, this fits into the ridge of this pentagonal 

 plate. 



Thus it can be seen that lateral movement of the head can take 

 place to a degree ; while upward movement is rendered almost 

 impossible by the close apposition of the bones. On the other 

 hand downward movement can take place to a considerable degree. 



Axis : The odontoid process is represented by a sub-conical pro- 

 jection proceeding forward from the centrum. Three articular 

 facets surround its base, the upper ones articulating with the lateral 

 surfaces of the atlas, the inferior with the hypapophysis. The 

 pedicles are short and straight, while the laminse are quadrilateral, 

 their antero-posterior and lateral measurements being equal. The 

 neural spine is short and conical, and the neural canal is more 



