60 



.i.u/!;/i'/r.i.\ Ml si'jiwr cvide leaflets 



36), witli its short crown, clearly defined base line and flaring roots. 



Wear and movement of premolars and molais can be studied very 

 readily fiom the skulls on exhibition, three of which are shown in fi<!;ure 

 37. 



I'or the present we will consider only the lower teeth, which will 

 ai)pl\ ill a «j;eneral way to the upj^ei' as well. The ^;rowth of the tooth 

 bejiins at the »iiindin^ surface, inside the alveolar cavity, and j)roceeds 

 toward the root, the tooth constantly moving upward, eruptin<j; and be- 

 «iinnin«i; to wear off before^ even the crown is complete. 



I''i«iure 37.1 shows the skull of a horse a))out five years old. The 

 deciduous set has been shed and the i)ermanent teeth are all in u.^e, 

 thoutih the wolf tooth (/;. ni. t) is not present in this siKM'imen. 



The crown of p. ni. t, the last tooth in the jirinding set to reach the 

 wearintj; line, is now fully grown, having already lost about half an inch 

 from wear. It now measures three and a half inche.s, making a total 

 length of four indues to be slowly moved upward and worn away. The 

 roots are just beginning to develop at the base of the crown. The next 

 tooth back of this, m i , is the first permanent tooth to appear, hence the 

 oldest one in the mouth. The crown is worn down much shorter than 

 that of p. m. T, and the roots are quite evident, though still incomplete. 



In figure 37B, showing a speeimen about eight years old, the crowns 

 have all been perceptibly reduced by wear, and the roots are all more or 

 less developed, those of m. t being almost completely grown. 



The oldest skulP in our exhibit is a specimen from a horse thirty- 

 nine years old, figure 37C. The crowns are almost entirely worn away. 

 Some of the roots are very much elongated, while others are thickened by 

 an extreme reenforcement of cement . The molars are very much inclined 

 forward, particularly ///. t, which is so worn as to almost separate the two 

 roots. In the upper set, p. m. - is represented only by irregularly shaped 

 lumps of cement which surround the last fragments of roots, prolonging 

 to the utmost their very much impaired service. - 



ERUPTION OF THE TEETH OF THE HORSE 



THE calcification of all the deciduous teeth and also m. \ begins 

 b(>f()re birth. When the colt is born, d. i. i and d. ni. I and f are 

 very near the surface of the gum, and generally erupt within two 

 or three days; d. m. 4 is apt to follow during the first month; d. i. s, 

 the last deciduous tooth to erupt, makes its appearance as late as the 

 eighth or tenth month. The three deciduous molars seem very large for 



'Since wiitiiiir, a skull 42'? years old has been olUaiiied, Siieciiiieii No. KiS. on exhibition. 

 -Speciiuen Xo. l'.i'2 in wall case shows interesting examples of reenforcement by cement in extreme 

 old age. 



