934 



THE ORGANS OF DIGESTION. 



first upper bicuspid being frequently bifid. The first upper bicuspid is usually the 

 largest of the series. 



The molar teeth (multicuspidati ; or grinders) are the largest teeth of the den- 

 ture. They are adapted by their forms for the crushing and grinding of the food. 

 They are twelve in number, six in each jaw, three being placed posterior to each 

 second bicuspid. 



The crowns are cuboidal in form, are convex buccally and lingually ; they are 

 flattened mesially and distally. They are formed by the fusion of three primitive 

 cuspids in the upper and four in the lower. To these are added in the first and 

 second upper molars a disto-lingual tubercle, and in the first and third molars of 

 the lower jaw a disto-buccal tubercle. The unions of the primitive forms are 

 marked by sulci. The necks of these teeth are large and rhomboidal in form. 



The roots of the upper molars are three in number one large lingual and two 

 smaller buccal roots. In the lower, two roots are found, a mesial and a distal, each 

 of which is much flattened from before backward. 



The first molar teeth are the largest of the dental series : they have four cusps 

 on the upper and five in the lower three buccal and two lingual. 



The second molars are smaller ; the crown of the upper is compressed until the 

 disto-lingual cusp is reduced. The crowns of the lower are almost rectangular, with 

 a cusp at each angle. 



The third molars are called the wisdom teeth (denies sapientice) from their late 

 eruption : they have three cusps upon the upper and five upon the lower. The 

 three roots of the upper are frequently fused together, forming a grooved cone, 

 which is usually curved backward. The roots of the lower, two in number, are 

 compressed together and curve backward. 



Right upper. 



Temporary Teeth (Figs. 553 and 557). 



The temporary or milk teeth are smaller, but 

 resemble in form those of the permanent set. The 

 neck is more marked, owing to the greater degree 

 of convexity of the labial and lingual surfaces of 

 the crown. The hinder of the two temporary mo- 

 lars is the largest of all the deciduous teeth, and is 

 succeeded by the second bicuspid. The first upper 

 molar has only three cusps two labial, one lin- 

 gual ; the second upper molar has four cusps. The 

 first lower molar has four cusps ; the second lower 

 molar has five. The roots of the temporary molar 

 teeth are smaller and more diverging than those 

 of the permanent set, but in other respects bear a 

 strong resemblance to them. 



Lin- 



Arrangement of the Teeth. 1 



The human teeth are arranged in two parabolic arches, the upper arch being 

 larger, its teeth overlapping the lower. The average distance between the centres 

 of the condyles of the inferior maxillary bones is about four inches, which is also 

 the distance from either of these points to the line of junction between the lower 

 incisor teeth. Whether the jaw be large or small, the equilateral triangle indicated 

 is included in it ; the range of size is between 3^" 4^-". 



Owing to the smaller sizes of the lower incisors, the teeth of the lower jaw are 

 each one half a tooth in advance of its upper fellow, so that each tooth of the dental 

 series has two antagonists, with the exception of the lower central incisors and 

 upper third molars (Figs. 558, 559). 



The grinding faces of the upper bicuspids and molars curve progressively up- 

 ward and point outward, the first molar being at the lowest point of the curve, 



1 After Dr. W. G. A. Bonwill. 



