52 THE HEAD. 



onites witli the frontal, and forms a strong- arch — ^the zygomatic — 

 distinctly to be felt at the side of the head, immediately above 

 the eye. This arch is designed to protect the upper part of the 

 lower jaw, the motion of which may very plainly be seen be- 

 neath it when the horse is feeding. 



At the base of the arch is an important cavity not visible in 

 the cut, receiving into it, and forming a joint with, the head of 

 the lower jaw — it will be presently described. 



Having reached the base of the temporal bone, it is found 

 united to the parietal, not by a simple suture, as the lower part 

 of the frontals, or the bones of the nose (see fig. a and j. Fig. 2), 

 nor by a dove-tailed suture, as the upper part of the frontals (see 

 the same cut), but it is spread over the parietal in the form of a 

 large scale, and hence, as before observed, called the sqitamous 

 portion of the temporal bone. In fact, there are two plates of 

 bone instead of one. Was there design in this ? Yes, evidently so. 

 In the first place, to increase the strength of the base of the zygo- 

 nuitic arch. This extensive union between the temporal and parie- 

 tal bones, resembles the buttress or mass of masonry attached to 

 the base of every arch, in order to counteract its lateral pressure. 

 The concussion, likewise, which might be communicated by a 

 blow on the top of the arch, is thus spread over a large surface, 

 and consequently weakened and rendered comparatively harmless ; 

 and that surface is composed of the union of two bones of dissimi- 

 lar construction. The hard stonij structure of the parietal is 

 very different from the tougher material of the temporal ; and 

 thus, as a finger acts on a sounding-glass, the vibration commu- 

 nicated to the temporal is at once stopped, and the brain receives 

 no injury. 



There is another proof of admirable design. Where is this 

 iqiiarnous portion of the temporal bone situated ? On the side 

 of the head. And what is the figure of the cranium or skull, 

 and principally that part of it which contains the cerebrum or 

 brain ? It is an elhptical or oval arch (see fig. m, n, o, Fig. 3). 

 If pressure is made on the crown of that arch — if a blow is re- 

 ceived on the suture between the parietals sufficient to cause 

 the elastic materials of which the skull is composed to yield — 

 the seat of danger and injury is at the side. If a man receives 

 a violent blow on the crown or back part of the head, the frac- 

 ture, if there is any, is generally about the temple, and the ex- 

 travasation of blood is oftenest found there. The following figure 

 will explain this : — 



Let the line ABC represent an elliptical arch, composed af 

 elastic materials. Some force shall be applied at B, sufficient 

 to cause it to yield. We cannot compress it into smaller compass ; 

 but iust in proportion as it yields at B, will it spur or bulge out at 



