362 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



A. Descriptive. 



I. — The Skull. 

 Plate XXII, Figs 1-3. 



The basioccipital (bo.) forms the entire centrum of the 

 condyle for the attachment of the vertebra. The suture 

 separating it from the exoccipital runs longitudinally directly 

 through the middle of the auditory capsule until it reaches 

 a transverse suture at right angles to it, separating the basi- 

 occipital and exoccipital from the prootic. 



The exoccipitals (eo.) alone border the foramen magnum, 

 meeting slightly above it. Below it, a little within the 

 mouth of the foramen between their articular facets, above 

 the basioccipital, they meet as a bridge of bone. 



The supraoccipital (so.) is interposed posteriorly between 

 the exoccipitals, separating them except at their posterior 

 upper corners. It extends anteriorly to the frontals, but is 

 so covered by the parietals that only a small portion of it is 

 visible. 



The parietals (p.) extend laterally over the supraoccipital 

 and meet in an irregular suture. Posteriorly they overlie 

 and cover the upper portion of the epiotics. Each bears 

 two large spines, the posterior of which is pierced at its 

 base by a large transverse foramen. 



The epiotic (epo.) is a pyramidal bone with a rather large 

 articular surface for the articulation of the superior limb of 

 the post-temporal which is strongly wedged in between it and 

 the overhanging parietal. 



The pt erotic (pto.) forms the usual posterolateral wing of 

 the skull. It bears a large spine on its upper surface, and 

 to its under side is attached the posterior part of the head 

 of the hyomandibular. 



The opisthotic (opo.) is a scale-like bone overlying the 

 suture between the pterotic and exoccipital on the lower 

 aspect of the skull. The inferior limb of the post-temporal 

 is attached to it. 



