TEMPORARY TEETH. 713 



The crown is small and rounded, and furnished with three tubercles. 



The root is generally single, short, conical, slightly curved, and grooved so 

 as to present traces of a subdivision into three fangs in the upper, and two in 

 the lower jaw. 



TEMPORARY TEETH. 



The Temporary, or Milk Teeth, are smaller, but resemble in form those of 

 the permanent set. The hinder of the two temporary molars is the largest 

 of all the milk teeth, and is succeeded by the second permanent bicuspid. The 

 first upper molar has only three cusps, two external, one internal : the second 

 upper molar has four cusps. The first lower molar has four cusps : the second 



Fig. 386. The Temporary, or Milk Teeth. External View. 



Lower Jaw 



Canine 



Incisors 



lower molar has five. The fangs 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. 



Structure. On making a vertical section of a tooth (Fig. 387), a hollow cavity 

 will be found in the interior. This cavity is situated at the base of the crown, 

 and is continuous with a canal which traverses the centre of each fang, and 

 opens by a minute orifice at its extremity. The shape of the cavity corre- 

 sponds somewhat with that of the tooth : it forms what is called the pulp cavity, 

 and contains a soft, highly vascular, and sensitive substance, the dental pulp. 

 The pulp is richly supplied with vessels and nerves, which enter the cavity 

 through the small apertures at the point of each fang. 



The solid portion of the tooth consists of three distinct structures, viz., ivory 

 (tooth-bone, or dentine), which forms the larger portion of the tooth; enamel, 

 which covers the exposed part, or crown; and the cortical 

 substance, or cement (crusta petrosa), which is disposed as a 

 thin layer on the surface of the fang. 



The Ivory, or Dentine (Fig. 388), forms the principal mass 

 of a tooth; in its central part is the cavity inclosing the pulp. 

 It is a modification of the osseous tissue, from which it differs, 

 however, in structure and chemical composition. On exami- 

 nation with the microscope, it is seen to consist of a number 

 of minute wavy and branching tubes, having distinct parietes. 

 They are called the dental tubuli, and are imbedded in a dense 

 homogeneous substance, the intertubular tissue. 



The dental tubuli are placed parallel with one another, and 



Fig. 387. Vertical 

 Section of a Mo- 

 lar Tooth. 



Pant 



