182 A MANUAL OF DENTAL ANATOMY. 



of the ramus at first remaining oblique, though the angle of 

 the jaw becomes developed as a stout process for the attach- 

 ment of muscles. At the age of six months the syniphysis 

 is still well marked, and the mental prominence first becomes 

 noticeable. 



FIG. 78 



An additional bony crypt for the first permanent molar 

 has also appeared, though its separation from that of the 

 second temporary molar, from which it was at first in no 

 way distinct, is yet incomplete, especially in the lower jaw. 

 In the upper jaw the first permanent molar crypt has no 

 posterior wall ; bony cells for the permanent central incisors 

 are well marked, but those for the laterals are mere deep 

 pits in the palatine wall of the crypts of the temporary teeth. 



At the age of eight months, or thereabouts, the process 

 of the eruption of the teeth, or "teething," has fairly set in ; 

 anchylosis has taken place at the symphysis of the lower 

 jaw, the mental prominence is well marked, and in the upper 

 jaw the antrum has become a deep depression, extending 

 under the inner two-thirds of the orbit. 



Postponing for the moment the consideration of the erup- 

 tion of the teeth, in order to follow up the growth of the 

 jaws, it becomes necessary to take some fixed points as 

 standards from which to measure the relative alteration of 

 other portions of the bone. In most bones, processes for 

 the attachment of muscles would be very unsuitable for the 

 purpose, because they would alter with the general altera- 



(*) Lowci* jaw of a niue months foetus. 



