296 SPLANCHNOLOGY. 



enamel pulp. The process of calcification now commences. A. 

 thin lamina or cap of dentine is first developed on the outer and 

 most prominent part of the pulp, from its covering membrane ; 

 this continues to be formed by the substance of the pulp, which 

 gradually decreases as the dentine increases, the enamel being, 

 at the same time, deposited in crystals from its own peculiar or 

 outer pulp. The cementum also forms pari passu, from the 

 calcification of the periodontal membrane lining the sac. When 

 calcification of the dental textures is sufficiently advanced, the 

 tooth makes its way through the gum, which is absorbed, as the 

 crowns are forced upwards by the growth of their fangs. The 

 septa or divisions between the dental sacs now ossify, and con- 

 stitute the alveoli. As growth continues, the base of the pulp 

 contracts and forms the neck. The dental sac now elongates, and 

 gradually becomes less, owing to the formation of dehtine on its 

 outer surface, until only a small cavity is left in the centre, in 

 which rests the pulp and its vessels. In the molars, every point on 

 the crown has a separate cap of calcification. These enlarge, and 

 finally meet. In the formation of the molar fangs the pulp divides, 

 ossification in each section proceeding as in a singie-fanged tooth. 

 The permanent teeth are developed like the temporary ones. 

 As the permanent tooth continues to grow, it gradually presses 

 on the milk tooth, and ensures absorption of its roots, until the 

 entire fang becoming removed, the crown of the milk tooth falls 

 out, and the permanent tooth appears above the gum. The 

 remaining permanent teeth, the three posterior molars in each side 

 of either jaw, are developed thus : — Behind the third molars 

 there is a portion of the dental groove unobliterated, which forms 

 a cavity,- called the posterior cavity of reserve, in which a papilla 

 appears, and undergoes the same change as that of the temporary 

 teeth, forming the rudiment of the fourth molar. From this 

 cavity is developed a second follicle for the fifth, and from this 

 the follicle of the sixth or last molar. 



PHAEYNX. 



The pharynx is a musculo-membranous cavity common to 'the 

 digestive and respiratory canals. Somewhat cylindrical in the 

 horse, it extends obliquely downwards and backwards, and lies 

 behind the velum palati, which separates it from the mouth, an4. 

 forms its anterior wall. It is attached superiorly to the base of 



