110 



THE SENSORIAL FUNCTION. 



e o 

 dd 

 e e 

 ff 



y a 



h h 



1 J 

 kk 



I I 



a prolongation of the brain, and thus connected with sensation and voluntary 

 motion, governing all the involuntary motions of the frame, and by power from 

 which the heart beats, and the lungs heave, and the stomach digests ; and one 

 other system of nerves — the ganglionic — presiding over the functions of secretion 

 and of nutrition, and the repair and the welfare of the frame generally. 



The following cut represents the head of the horse divided into the numerous 

 bones of which it is composed, and the boundaries of each bone clearly marked 

 by the sutures which connect it with those around. 



The upper and broadest part is the cranium or skull in which the brain is 

 contained and by which it is protected. It is composed of nine bones : the two 

 frontals, a a; the two parietals, c c ; the two temporals, d d; the occipital, g, 

 and the ethmoid and sphenoid, which will be found delineated at figs, k and I, 

 and which will be better seen in the cut in the next page. 



a a The frontal bones, or bones of the forehead. 

 b b The supra-orbital foramina or holes above theorbit,fhrough 

 which the nerves and blood-vessels supplying the fore- 

 head pass out. The small hole beneath receives the 

 vessels which dip into and supply the bone. 

 The parietal bones, or walls of the skull. 

 The temporal bones, or bonei of the temples. 

 The zygomatic, or yoke-shaped arch. 

 The temporal fossa, or pit above the eye. 

 The occipital bone, or bone of the hinder part of the head. 

 The orbits containing and defending the eye. 

 The lachrymal bones belonging to the conveyance of the 



tears from the eyes. 

 The nasal bones, or bones of the nose. 

 The malar, or cheek-bones. 



The superior maxillary, or that portion of the upper jaw 

 containing the molar teeth or grinders. 

 m m The infra-orbital foramen — a hole below the orbit, through 

 which pass branches of nerves and blood-vessels to sup- 

 ply the lower part of the face. 

 n n The inferior maxillary, the lower part of the upper jaw- 

 bone — a separate bone in quadrupeds, containing the 

 incisor or cutting teeth, and the upper tushes at the 

 point of union between the superior and inferior max- 

 illaries. 

 o The upper incisor or cutting teeth. 



p The openings into the nose, with the bones forming the 

 palate. 



There is an evident intention in this division of the head into so many bones. 

 When the foetus — the unborn foal— first begins to have life, that which after- 

 wards becomes bone, is a mere jelly-like substance. This is gradually changed 

 into a harder material — cartilage ; and, before the birth of the animal, much 

 of the cartilage is taken away by vessels called absorbents, and bone deposited 

 in its stead. In flat bones, like those of the head, this deposit takes place in 

 the centre, and rays or radiations of bone extend thence in every direction. 

 Then, by having so many bones, there are so many centres of radiation ; and, 

 consequently, the formation of bone is carried on so much the more rapidly, 

 and perfected at the time when the necessities of the animal require it. At the 

 period of birth, however, this process is not completed, but the edges of the 

 bones remain somewhat soft and pliant, and therefore, in parturition, they 

 yield a little and overlap each other, and thus, by rendering the birth mora 

 easy, they save the mother much pain, and contribute to the safety of the foal. 



The first of these bones, or the first pair of them, occupying the broad expanse 

 of the forehead, are called the frontal bones, a a. They are united together by 

 a most curious and intricate dove-tailing, to defend from injury the brain which 



