110 THE STKUCTUKE OF THE HOESE. 



again at the hinder part of the face. This is called 

 the " zygomatic arch," and is almost constantly pres- 

 ent in the skulls of mammals. 



Standing out as it does, it allows the npper part 

 of the under jaw to work beneath it, and its onter 

 surface affords a very advantageous point of attach- 

 ment to a great muscle (masseter), to be spoken of 

 presently. The side of the brain-case between this 

 and the top ridge of the sknll is called the " tempo- 

 ral fossa" (t). Though bounded by raised ridges all 

 round, enough to give it the general character of a 

 depression or fossa, its floor is formed by a convex 

 surface, the side of the actual brain-cavity. The 

 fossa is mainly filled in life by one of the muscles 

 (temporal) which close the jaw, but its anterior part 

 contains much fat, the loss of which in old horses 

 gives rise to the characteristic depression seen in 

 them above the eye. Farther forward is the cavity 

 (o) } of almost circular outline, in which the eyeball 

 is lodged, called the " orbit," with very sharply de- 

 fined and complete outer and hinder margin, formed 

 by a bridge of bone passing upwards from the zygo- 

 matic arch to join the "frontal," or forehead-bone. 

 This is a point in the anatomy of the horse to be es- 

 pecially noticed, as it gives a very characteristic ap- 

 pearance to his skull. The interest of this bridge of 

 bone, dividing the orbit from the temporal fossa, is 



