46 PRACTICAL ANATOMY. 



alveolar border abruptly constricts the necks of the 

 teeth, but does not fit around them tightly ; the teeth 

 can be rattled in their sockets in the recently cleaned 

 skull ; this, of course, under normal circumstances, can- 

 not be done, as the soft structures serve to pack the 

 teeth firmly in position. 



The superior maxillary develops by four centres, 

 which appear at the beginning of the third month. One 

 centre serves for the development of the nasal and facial 

 portions, including the anterior wall of the antrum. A 

 second centre is for the development of the malar and 

 orbital portion, with the lateral and posterior parts of the 

 bone. From a third centre the inner surface and pos- 

 terior portion of the palatine process develop. The an- 

 terior portion of the palate process and the anterior part 

 of the bone up to the canine tooth are developed by a 

 separate centre. The line of junction between this in- 

 cisive portion and the rest of the bone occasionally per- 

 sists as a suture, a condition which in some of the lower 

 animals is the rule, forming a separate piece of bone, the 

 intermaxillary, particularly well seen in the skulls of 

 sheep. When this centre does not appear, a cleft exists 

 at the anterior part of the roof of the mouth, constitut- 

 ing one form of harelip and cleft palate. 



THE LACHRYMAL BONE. 



The lachrymal is a delicate, flat, quadrilateral bone, 

 situated at the inner wall of the orbit; articulating ante- 

 riorly with the nasal process of the superior maxillary, 

 above with the orbital plate of the frontal, posteriorly 

 with the os planum of the ethmoid, and inferiorly with 

 the orbital plate of the superior maxillary, and the in- 

 ferior turbinated bone. It is about four lines in width 

 by eight lines long. It is translucent, and, other than 



