Motor System — Muscles and Skeleton 



123 



Fig. 120. General plan of the skull. With the exception of some elements of 

 comparatively rare occurrence, all the bones that occur in any skull are indicated 

 in the diagram. But the skull of no one animal would contain all the bones there 

 shown. The figure represents a side view. All the elements of one half of the skull, 

 including those that are actually dorsal or ventral in position, are brought into 

 view. The diagram aims to express correctly the essential facts regarding the 

 positional relations of the elements. It conveys nothing as to their form and size. 

 Dermal bones are cross-lined. The numbers refer to the table on p. 122. 



In this diagram the general relations of cranium and visceral arches are such 

 as obtain in a bony fish. In higher vertebrates the bones of the upper jaw are 

 annexed to the floor and side regions of the cranium, more or less enclosing and 

 obscuring the true cranial elements (see Fig. 121). 



B 



Fig. 121. Diagrams showing the relations of the jaws to the cranium in a reptile. 

 The true cranial elements and the elements of the lower jaw are not fully indicated. 

 (A) Side view. (B) View of the roof of the mouth. 



