63 

 As is here seen, when the crown has been removed, 

 the permanent molar is well up, although it occupies 

 the same place, and fills the same alveolar cavity 

 which the temporary molar originally held. The 

 horse incisors do not occupy the same cavities in 

 which the milk incisors were placed, but are de- 

 veloped in cells formed especially for their reception, 

 and come up rather behind than absolutely under the 

 primary teeth. The form of the anterior part of the 

 jaw in the foal admits of such an arrangement, and 

 its greater comparative bulk gives all the space that 

 was required. The space, however, between the 

 branches of the lower jaw where the molars are de- 

 veloped, is filled by important muscles ; and while 

 any thickening externally would deteriorate from the 

 symmetry of the head, any internal enlargement 

 would have interfered with the free motion of the 

 tongue and hyoideal appendages, the movements of 

 both being as essential to perfect mastication as the 

 presence of the teeth themselves. Hence the grinders 

 are in their development regulated by a different law 

 to the incisors ; nor is the ordinization which declared 

 the first should be well up, and the last scarcely to 

 be seen when the period for casting off the tempo- 



