36 



CLASSIFICATION 



broad - crowned cheek-teeth, twenty in number, of which the 

 first eight are known as bicuspids or premolars, while the 

 remainder are called molars. All this may be expressed by a 

 dental formula as follows : — 



I. = 



c. = 



= ^—^, p.m. = ?— ?. 



2-2 I - I -^ 2-2 



\i. = incisor, c. = canine, p.m. = premolar, m 



m. =- — - = X2. 

 3-3 •* 

 : molar.] 



Each fraction corresponds to one kind of teeth, the numerator 

 representing upper and the denominator lower ones, while the 

 dashes above and below mark the distinction between teeth on 

 the right and left side. Since these structures are symmetrically 

 arranged it is only necessary to represent those of one side, and 

 so it is convenient to shorten the formula to — 



X 2 = 32. 



2.1.2.3 



In the first or milk set the incisors, canines, and premolars are 

 represented respectively by milk incisors, milk canines, and milk 



molars, while the molars of the per- 

 manent set have no predecessors. 



Fig. 12. — The Salivary Glands 

 pp', Parotid: 5?«, sub-maxillary. d\% 

 placed below the duct of the parotid. 



Fig. 13. — Relations of the Stomach to the Liver, 

 Pancreas, and Spleen 



osp. Stomach; d, small inLestine; l, liver; g^ gall- 

 bladder; y^ placed toleftof bile-duct: A, i> pancreas: 

 sjt, spleen ; w, placed below blood-vessels of spleen ; 

 a and », blood-vessels. 



3. Digestive Glands (figs. 12 and 13). — These elaborate or 

 secrete different fluids, which act chemically upon the food. 

 Opening into the mouth-cavity are three pairs of soft masses, the 

 salivary glands, which secrete the spittle or saliva. One pair is 

 placed in front of the ear (parotid), and it is these structures which 

 swell up and become painful in cases of mumps. A second pair 

 (sub-maxillary) are placed between the halves of the lower jaw. 

 while the third and much smaller pair (sub-lingual) are imbedded 

 in the deeper part of the tongue. 



