752 EXAMINATION FOE AGfE. 



Irregularity in the Respective Size of the Upper 



and Lower Jaw. 



The chief irregularity under this heading, is that of parrot- 

 mouth," in which the teeth of the upper jaw project, to a con- 

 siderable extent, beyond those of the lower jaw (Figs. 202, 203, 

 and 204). Although parrot-mouth in a fully developed form, 

 appears as a rule only in old horses; we may commonly see, even 

 in five and six year olds, the upper central incisors projecting a 

 little beyond the lower ones. This tendency is slightly shown in 

 Fig. 242 ; and in a well-marked manner in Fig. 256. It is 

 almost certain that animals possessing this peculiarity would 

 become parrot-mouthed in their old age. Surgical interference 

 is generally required in well-developed cases of parrot-mouth; 

 because this condition greatly diminishes the animal's power of 

 seizing and cutting his food with his front teeth. 



It is not a very rare occurrence to find the lower jaw slightly 

 in advance of the upper one, which is a peculiarity that renders 

 an animal " under-hung." I have seen this condition in a horse, 

 and also in a mule, existing to such an extent that the lower front 

 incisors alniiost completely hid fro'm view the upper front incisors. 

 The posterior aspect of the former was a good deal worn away by 

 friction with the anterior face of the latter. 



Irregularities in the Teeth. 



We sometimes find one or more supernumerary permanent incisor 

 teeth (Figs. 205, 206, 207, and 208), especially in the upper jaw. 

 These teeth form a more or less complete row behind the ordinary 

 incisors. They are entirely different from the stumps of milk 

 teeth which are sometimes retained (Fig. 209) ; are inserted more 

 or less firmly in the jaw; and interfere to a greater or less degree 

 with the regularity of the respective positions taken up in the 

 jaw by the ordinary incisors. 



In rare cases, the incisors assume irregular forms even in young 

 mouths. 



The presence of a supernumerary molar is very rare, in a horse. 

 Fig. 210 shows this peculiarity on the near side of the lower jaw 

 of a ten-year-old animal. As it could not be a case of atavism 

 (reversion to a more or less remote ancestor), it was probably 

 one of dichotomy (splitting into two parts). 



The irregularities due to crib-biting have been alluded to on 

 page 556. 



