THE TEETH 



421 



FIG. 343. 



Incisors. 



Canine. 



Second Molar. 



more distinct. When unworn, the middle cusp appears to be longer 

 than the corresponding cusp of the permanent teeth. 



The lower deciduous canine (Figs. 342, 343) is more vertical than 

 the permanent tooth ; it resembles the upper deciduous canine, but the 

 angle on the anterior border is often de- 

 veloped into a distinct cusp, which strikes 

 against the outer side of the crown of the 

 third upper incisor. 



The first lower deciduous molar is the 

 tooth which is posterior to the lower canine 

 and separated from it by a long diastema, 

 where the jaw is excavated for the passage 

 of the upper canine. It resembles the 

 permanent first premolar which replaces 

 it. It is smaller, however, and its crown 

 is more acute and more deeply incised ; the 

 taloii is well developed. 



The second lower deciduous molar, 

 the last in the jaw, differs from the pre- 

 molar which replaces it in being a sec- 

 torial tooth. It closely resembles the 



permanent sectorial; its crown, however, presents a more elevated 

 posterior cusp on the cutting blade, behind this a smaller cusp, and a 

 decided talon on the cingulum. 



The relations between the upper and lower deciduous teeth are 

 somewhat different from the relations between the upper and lower 

 permanent teeth. The transverse width of the row of upper incisors 

 is often very little greater than the width of the row of lower incisors ; 

 hence the lower canines are more vertical. In some cases, at least, 

 the lower incisors bite in front of the upper. The inner surface of 

 the large upper sectorial wears against the outer surfaces of both 

 lower molars ; the posterior outer part of the lower sectorial is sheared 

 by the prominent part of the anterior border of the tubercular third 

 upper molar. 



ERUPTION OF THE TEETH. 



The deciduous teeth begin to appear through the gums at about 

 the end of the second week after birth. They may be delayed, how- 

 ever, and the order of their appearance is undoubtedly subject to 



LEFT LOWER DECIDUOUS 

 TEETH. SUPERIOR ASPECT. 



