GO Mammalia. Digestive System. 



to tlie movements and mastication of tlieir coarse vegetable 

 food : tlieir secretion is more mucous than lubricating or 

 solvent. In sbort, the Parotid secretes tbe more fluid 

 >Saliva, wbich moistens in ordinary mastication the whole 

 mass ; the other glands secrete the slimy lubricating SaKva. 

 The Quantity of Saliva secreted by the Parotid {e.g. in Horse) 

 is in direct ratio to the dryness of the food and the difficulty 

 experienced in its mechanical division : while that secreted 

 by the Sublingual and Submaxillary flows in nearly equal 

 abundance, whether Mastication be exerted on dry or moist 

 forms of food. 



The Teeth present remarkable difierences in Structure, 

 Replacement, Form, and Number, which stand in close 

 relation with the whole economy, mode of life, and form of 

 the species ; but generally agree in limits of Situation and 

 mode of Fixation. Structure. In some genera JSorny LamincB 

 take the place of teeth*; but, as a rule, hard unvascular Dentine, 

 and Cement, exist in every Mammalian tooth ; and Enamel, 

 though not constantly present, is generally found. In the 

 newly formed tooth the Cement is always the outermost sub- 

 stance, and between it and the Dentine the Enamel is inter- 

 posed. The thickness of the coating of Cement in the adult 

 varies with the diet, being thin in those species that partake 

 of flesh or mixed diet, and thicker in those that feed on herbs. 

 According to the difierent arrangement of the Enamel, three 

 well vii^rk^di patterns of teeth are distinguishable : (i.) d. Simpli- 

 ces s. obducti, in which the Enamel forms an entire and uni- 

 form cap to the dentinal pulp ; (ii.) d. CompUcati s. semi- 

 compositi, in which the Enamel followed by the Cement is 

 inflected or penetrates into the Dentine and forms folds ; (iii.) 

 d. Lamellosi s. compositi, in which the folds of Enamel pene- 

 trate so far towards the root of the tooth as to divide it into 



* Bakena. OrnithorhTncus. 



