The Skull 109 



know them by their position relative to the brain open- 

 ing; the upper edge of the hole is always formed by the 

 supraoccipital, the lower by the basioccipital, the two 

 sides by the exoccipitals. 



Although many bones of the skull, such as the supra- 

 occipital, keep their names, whether found in salmon, 

 frog, lizard, bird, or man, others identical in position 

 have had new names given them. For instance, a small 

 bone directly in front of the eye is known as the lacrymal, 

 from its close relation to the tear-duct, but in fishes the 

 bone is called the preorbital, as a suggestion of fish-tears 

 would be rather absurd. 



We may find the dried ear-drum, or tympanum, 

 stretched tight across the entrance of the ear-cavities, 

 and if we break this, or even look carefully through the 

 transparent membrane, a long thin bone may be seen 

 beneath, extending backwards from the under surface of 

 the drum. This is the columella, or little column of 

 bone, and will have an interest for us later on. 



If we examine the way in which the upper and lower 

 mandibles or jaws are joined to the skull, we will find a 

 very ingenious arrangement; one very different from 

 that in ourselves. If the beak of a bird is to serve as 

 hand, lips, and mouth, it must be as free and movable as 

 possible, and instead of the upper jaw being fixed im- 

 movably to the skull, and the lower jaw swinging up 

 and down from it, we find that the upper jaw is attached 

 very loosely, while each side of the lower mandible hinges 

 upon a loose irregular-shaped bone, known as the quad- 

 rate. A long slender bone connects the quadrate with 



