556 NERVOUS DISEASES. 



incisors, so deep as to hurt his gum, or to reach the sensitive 

 portion of the teeth, he will try another pair of incisors ; and 

 so on. 



All these forms of wear, more or less complicate the determina- 

 tion of age by the teeth. 



Many horses, though free from the vice of crib-biting, wear their 

 teeth in a manner somewhat like that of cribbers, on account of 

 biting their manger,' etc., from irritability, when being groomed, 

 and sometimes from idleness. Here the question as to the animal 

 being a cribber, will be determined by the absence or presence, on 

 his part, of any attempt to swallow air. 



Cribbing, however, is not always characterised by wear of the 

 teeth. The support may be taken by the lips, chin, lower edges 

 of the branches of the jaw, and in exceptional cases by the throat 

 just below the larynx. 



When the cribber has obtained his required support, he will 

 take air into his partly-opened mouth, and having drawn in his 

 chin towards his breast, and arched his neck, he will make a 

 convulsive effort to swallow the mouthful of air ; and at the same 

 time will, as before said, emit a characteristic grunt. By drawing 

 his tongue backwards and upwards, he will raise the soft palate, 

 and will close the air-passage which leads into the nostrils, and 

 will also close the entrance into the windpipe. 



The windsucker, generally, begins by backing away from the 

 manger ; poking his nose out ; sucking air into his mouth, as may 

 be seen by the forward and backward movements of his lips, which 

 he sometimes smacks together, or rolls them from one side to the 

 other as if he was trying to form in his mouth a bolus of food in 

 order to swallow it. At the same time, he places his tongue 

 against his palate. He may stop at this point, in which case his 

 effort will end only in the swallowing of saliva, which does not 

 satisfy him. In well-developed cases, he draws in his chin towards 

 his breast, arches his neck, and violently contracts the muscles of 

 deglutition in the same manner as the cribber, in his effort to 

 swallow the mouthful of air, which, on account of its extreme 

 compressibility, l>e finds difficult to " get down." It has often 

 been remarked that an old cribber or windsucker may be known 

 by the unusually large development of the muscles (sterno- 

 inaxillaris and omo-hyoideus, among others) which the practice 

 of his vice calls into play. 



An instance is recorded of a foal practising it at three moriths, 

 and others at six months old. 



CRIBBING AND WINDSUCKING BY ANIMALS OTHER 

 THAN THE HORSE. — Several cases of cribbing and windsucking 



