Book VII. 



ANATOMY OF THE HORSE. 



893 



behind them is lodged the anterior and inferior portion of the brain. A division of their bony surfaces 

 forms two cavities called the frontal sinuses, which are lined by the nasal or smelling membrane 



a 

 615 



throughout. The union of these two bones is by means of the sagittal suture. The remainder of the 

 bones of the skull are the two parietals, the two temporals, divided into a squamous and petrous portion, 

 within the latter of which is situated the internal ear ; and to the former the posterior or lower jaw arti- 

 ticulates. The sphenoid and ethmoid bones are hollow and irregular, serving to intersect and attach the 

 others ; and also to assist by their cavities in extending tbe pituitary or smelling membrane. 



563'2. The hones of the face are ten pairs and two single bones. The nasal (c) pair within their union, 

 hold the septum narium or long cartilaginous plate which separates one nostril from the other. These 

 bones also greatly assist to extend the surface of the smelling organ. In the old heavy breeds, it was. 

 very common to "see these bones arched outwards ; but in the improved breed, particularly in those ap- 

 proaching full blood, it is not uncommon to find them slightly curved inward. The fossse within these 

 bones are the principal seat of glanders. The two angulars form a considerable portion of the orbits of 

 the eyes. The two malar, jugal, or cheek bones occupy also a portion of the orbits. The superior maxillary 

 bones (c) are the largest of the face bones, and contain all the upper molar teeth. The inferior or inter- 

 7naxillary bones {d) are wanting in man, in whom the face is short : these bones concur with the former 

 in forming alveoli or sockets for lodging the teeth. Tlie superior palatines, the inferior palatines, the 

 pteregoids, the two anterior, and the two posterior turbinated bones, with the vomer or plough sharCy 

 make up the remaining facial bones, with the exception of the posterior maxillary or lower Jaw bone (/), 

 which on its anterior edge is pierced to lodge the teeth ; at the upper part it extends it.self into two angular 

 branches, each of which ends in two processes, and an intermediate groove. The most superior of these 

 processes articulates with the upper jaw. This bone throughout shows the most admirable mechanism ; 

 the molar or grinding teeth, on whom most is dependent, and whose exertions are greatest, are placed 

 near the centre of motion ; and as the upper jaw in most animals is fixed, or nearly so, it was necessary 

 that the lower should have considerable extent of motion for the pur|)Ose of grinding ; and it is accord- 

 ingly so formed as to admit of motion in every direction. The os hyoidcs is a bone situated within the 

 head at the root of the tongue, to which it serves as a support, and for the attachment of mu.sdes. 



5633. The teeth of the horse are the hardest and most compact bones of the body. There are usually forty 

 of them in the horse, and there are thirty-six in the mare; in which latter, the tushes are usually wanting. 

 In anatomical language, they are divided into incisorcs, cuspidati, and molares, or according to the 

 language of farriers and horsemen, into twelve nippers (fig. Gli a, b, c), tour tushes (d d), and twenty- 

 four grinders, which numbers are equally dividetl between the two jaws. The teeth are received into in- 

 dentations or sockets between the bony plates of the jaw, called alveoli, by cone like roots. The bodies 

 of the teeth are principally composed of two substances, one of the nature of common bone^ giving bulk 

 and form, and one of extreme hardness, placed in man and carnivorous animals, wholly without the 

 teeth to give strength and durability : but in the horse and other granivoras, the lattev' particularly, is 

 placed in the grinders, in perpendicular plates, within the body of tiie teeth ; by which contrivance, a 

 rough grinding surface is kept up ; for the mere bony parts wearing fas-ter than the lamella; of enamel, 

 it follows that ridges remain to triturate the vegetable matter that passes between the teeth. 



5634. There are two sets of teeth, a temporaneous or milk set, and a permanent or adult set, in which 

 wise provision, man and most brutes participate. The milk set are some of them, as the molars, apparent 

 at birth ; there being usually six grinders in each jaw, three on each side in the new born foal, and which 

 number of this set is never increased. The nippers begin to ai)pear soon afterbirth, and follow a regular 

 order of succession until the animal is three or four months old ; at which time he begins to require sup- 

 port from herbage as well as milk. The temporaneous set, remove gradually one after another ; had they 

 all been displaced at the same time, or even had several of them fallen out together, the animal must 

 have suffered great inconvenience, and perhaps have been starved. This removal, which commences at 

 the age of two years and a half, and is completed between the fourth and fifth year, is effected by 

 the action of the absorbents on their fangs, and appears to be occasioned by the stimulus of the pres- 

 sure received from the growing teeth under them. For although these two sets appear with an interval 

 of some years between them ; yet the rudiments of both are formed at nearly the same jieriod, and both 

 sets may be thus seen in a dissected jaw. Regulated by the stimulus of necessity, as soon as the tempo- 

 raneous set falls out, the permanent appears : and that such appearance follows the necessity is evident ; 

 for a premature or accidental removal of the colts teeth is soon followed by the appearance of the others. 



