738 THE EXTERIOR OF THE HORSE. 



Let us add that the teeth of the shorter jaw, by increasing excessively in 

 length, are at times capable of injuring the corresponding parts of the opposite 

 jaw, the region of the barbs or the hard palate, according to the case. 



Our colleagues, Messrs. Weber and Mitaut,' have each observed an example 

 of inferior brachygnathism in which pressure was made on the hard palate 

 almost to the point of perforation. 



B.— Excess of Width of the Superior Incisive Arcade. — An excess 

 of width of the superior incisive arcade is quite frequently met. When the jaws 

 are closed, the latter overlaps the inferior arcade in front and upon the sides, 

 over its whole periphery. This is probably the beginning of what we will study 

 a little farther on under the name parrot mouth. 



7. Irregularities through Excess or from Insufficient Wear. 



§ 1. Incisor Teeth. 



In general, the incisors always preserve the same length of their 

 free part, although they diminish each year under the influence of the 

 friction which takes place upon their table. This is due to the fact that 

 the teeth are being constantly pushed out of their alveoli ; whence it 

 follows that what is at first a portion of the root will, in time, be 

 pushed out so as to constitute a part of the crown. Transverse mark- 

 ings, those of a rasp, for example, made at different heights on the 

 anterior face of these teeth, will ultimately disappear one after the 

 other. 



By experiments of this nature, Pessina^ has demonstrated an 

 annual wearing; awav of four millimetres of the tooth in t^ommon 

 horses, and only three millimetres in those that are well bred. H. 

 Bouley has verified the accuracy of these results in animals which 

 belonged to him. 



But there are some horses in which the teeth are too long, others 

 in which thev are too short. How can this be determined ? 



Nothing is more easy, since it is known, from the observations of 

 Girard, that the free part of the incisors, from the gum to the table, 

 has a mean length of fifteen millimetres. There are certain subjects, 

 nevertheless, in which this length varies according to the teeth ex- 

 amined. The same author has recognized that it is about eighteen 

 millimetres for the pincers, fifteen millimetres for the intermediates, 

 and thirteen millimetres for the corners. All these facts, which we 

 must remember, we will use presently. 



1 Weber et Mitaut, Bulletin de la Soci^t6 centrale de m^decine v6t^rinaire, in Recueil de 

 m6decine v^t^rinaire. ann^e 1876, p. 768. 



2 Pessina, Sul modo di conoscere dai denti I'eU dei cavelli. Translated from the German by 

 Luiggi Ferreri and revised by Giuseppe Antonio Cross, Milan, 1831, p. 24 and PI. ix. 



