SPECIAL FEATUEES IN STRUCTURE 495 



covers the root of the tooth; it consists of lameUated bone tissue, with 

 lacunae and caualiculi, but without haversian canals. It is covered with 

 periosteum, which is also reflected on to the walls of the alveolar cavity. 



In the incisor tooth of the horse there is no external dentine; the 

 crown of the tooth is enamel and crusta petrosa (fig. 662). In the molar 

 tooth affairs are different; crusta petrosa, dentine, and enamel all come to 

 the surface, and it is owing to the different degrees of hardness of these 

 substances that the necessary roughness of surface is maintained, as the 

 crown is worn away by use. 



Not only do the three structures of the teeth accomplish an important 

 purpose in the preparation of the food for digestion, but owing to variation 

 of colour they present a characteristic appearance which, taken 

 in connection with the form of the teeth, constitutes a dis- 

 tinguishing feature in the Equidct or horse family easily 

 recognized and quite reliable. 



With the aljove sketch of some of the special parts of 

 the skeleton of the horse it will l)e convenient to proceed 

 to the examination of some other characteristics which are 

 exliil)it('d by the animal. 



ColoUP may attract the attention of an observer even 

 more than variations in size and outline, and in many in- 

 Fig. 662. -Sec- stauccs tlic peculiarities which are recognized on the surface 



tion of Unworn -i n • i • i i t i 



Incisor of are more dennite, and certamly to the ordmary observer more 

 Adult Horse, intelligible, than the evidence which the anatomist obtains 



a, Dentine; h, p '" , ... c ■ , i 



Enamel; c, Ce- irom a closc examination ot internal parts. 

 mentum;(?,Puip Yov example, some six or seven species of the equine family 



may be distinguished by mere inspection of tlie markings on cer- 

 tain parts of the skin, the arrangement of the hair of the mane and the tail, 

 the size and the shape of the feet, the length of the ears, and the existence 

 or the al)sence of small horny callosities on the fore and hind extremities. 



The horse (Equtis cahallus, as it is known to naturalists) is variously 

 coloured, and to the observant eye has very curious markings, often spots 

 or stripes here and there. On the tail the hair is long, and grows from 

 the root to the tip of the organ, covering it completely. The mane also 

 is eminently characteristic, especially that part of it, the forelock, which 

 hangs between the ears over the forehead. 



Peculiar markings are also frequently seen in the form of a spot, 

 light or dark in colour, on the centre of the forehead. This mark varies 

 in form, is circular or oval, elongated or lozenge-shaped, and sometimes 

 occupies a considerable space, forming a kind of shield over the whole 

 front of the face. Blaze or race is the term given to this mark. 



