TTIl^ SENSORIAL PTTXCTIOX. 



145 



(liffereuce required by the different services and uses for which they were 

 destined. And farther, let it be remembered, that it is only by being well 

 acquainted with the structure and anatomy of the horse that we can 

 appreciate his shape and uses, or understand the different diseases to 

 which he is Hable. It is from the want of this that much of the mass of 

 ignorance and prejudice which exists as to the diseases to which he is 

 subject is to be referred. 



We begin with the head, containing the brain and the most important 

 organs of sense. 



The following cut represents the head of the horse di^aded 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 twelve 

 bones, four pairs and four single ones : the four pairs are the two frontal, 

 two parietal, two squamous temporal, and two petrous temporal ; the 

 smgle are, the occipital bone, the sphenoid, the ethmoid, and the os triqua- 

 trum ; of these, the ones sketched in the plate are : — 



Tile frontal bones, or bones of the forehead. 

 The supra-orbital foramina or holes above the orbit, 

 through which the nerves and blood-vessels supplying 

 the forehead pass out. The small hole beneath receives 

 the vessels which dip into and supply the bone. 

 c c Tlie parietal bones, or walls of the skull. 

 d d The temporal bones, or bones of the temples. 

 e e 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 tiie 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 

 supply the lower part of the face. 

 « 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 tlie superior and inferior max- 

 illaries. 

 The upper incisor or cutting teeth. 



The openings into the nose, with the bones forming the 

 palate. 



a a 

 hh 



il 

 h h 



k k 

 II 



PP 



There is an evident intention in this di'^dsion of the head into so many 

 bones. When the foetus — ^the unborn foal — first begins to have life, that 

 which afterwards becomes bone, is a mere jelly-like substance. This is 

 gTadually 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 arc so many centres of radiation ; and, consequently, the formation 

 of bone is carried on so mrich 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 



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