FACE AND HEAD. 45 



jaw are the large passages through which the air 

 passes A x ,v, and are nearly hollow and form the 

 -back part of the bon}^ nostrils, but the cavities Y Y 

 are only there to allow of the bone being as light as 

 pos&ible, and as cavities are quite worthless. The 

 upper jaw forms an arch, having^ substantial 

 buttresses in the molar teeth and their bony sockets, 

 and whose span is of gigantic strength and ex- 

 tremely light from its hollow construction. 



If you notice a horse eating, you will see that the 

 lower jaw is pressed upwards against the upper jaw, 

 and moves from side to side. If the movement of the 

 lower jaw on the upper one were a simple up and 

 down movement, then the muscles could be per- 

 pendicularly placed and their bulk onl}' allowed for, 

 but seeing that the lower jaw has to be moved from 

 side to side, the muscles have to be obliquely placed 

 and so necessitates the branches of the jaw being 

 wide apart at their hindmost part. But the lower 

 grinders are somewhat narrower than the upper and 

 so allow greater range of motion in grinding, so that 

 breadth of the upper jaw is essential as well for 

 allowing free masticating power, as for power to 

 breathe freely through wide enough openings. 



32. — This then necessitates width between the 

 eyes, and width between the lower jaws. In the 

 figure illustrating this lesson you will find three 

 diagrams, B, C, B, representing front face views of 

 three degrees of width. What has been said will 

 explain why narrow-faced horses are often weakly, 



