742 A MANUAL OF VETERINARY PHYSIOLOGY 



Pig. 



In all these tables the periods given are those of eruption 

 only. The teeth are not fully developed for some time later, 

 which varies from four to six months in the horse to a month 

 in the pig and ruminant. Culley* noted that the central and 

 lateral temporary incisors attain their full growth in the foal 

 fifteen days after appearing, but that the corner teeth take 

 one and a half years to reach their full length. Without being 

 committed to this period, it is certain the corner temporary 

 teeth are much slower in coming into wear. 



The completion of dentition usually marks the age of maturity. 

 The uncastrated animal presents very distinctive features as 

 compared with the female — viz., greater bulk, a heavy crest and 

 neck, and a harsher voice ; the castrated horse more closely 

 resembles the mare. No such difference in the date of maturity 

 as is observable in the human family exists between the male 

 and female of the horse tribe. The mare arrives at maturity at 

 the same time as the horse, and the castrated animal is not 

 deficient in stamina, strength, or capacity for work. Moreover, 

 castration in the horse does not lead to a deposition of fat in the 

 body. 



Decay. — It is doubtful to what age a horse would live if not 

 subjected to domestication, but we may safely say that at 

 seventeen years old, which probably represents fourteen years' 

 work, the powers of life in the majority of them are on the wane, 

 though at this period some may be found in full possession of life 

 and vigour. These are probably cases of a survival of the fittest, 

 and cannot be taken as a general guide. As a broad rule it may 

 be stated that an old horse is liable to be killed by a hard day's 

 work, and in this sense he is certainly old at seventeen. A general 

 arterial degeneration is not marked at this period of life, and few 

 * Op. cit., p. 649. 



