BONES 



47 



Apparently the rate, time, and order of ossification are remark- 

 ably constant in the albino rat. Though only one litter was 

 used for each stage, comparisons of successive stages and the 

 constancy in litters seem to warrant this statement. 



TABLE HA 



Comparative table, giving time of first ossification of the skull bones in the rat and 

 man, during fetal life. (R. M. Strong, MS., '%4) 



Skull. Sutures: The following bones are more or less dis- 

 tinctly outlined by sutures at 525 days. 



Paired: Maxillae, premaxillae, nasals, palatines, f rentals, 

 parietals, jugals, petrosals, squamosals and tympanics. The 

 angle of the nasals with the frontals becomes more marked in 

 old rats, giving a "Roman nose" effect. 



Unpaired: The interparietal, supraoccipital, basisphenoid, and 

 presphenoid are all more or less distinct in the same specimen. 

 The interparietal is entirely outlined. The supraoccipital is 

 fused with the exoccipital. 



The dorsal surface of the skull of very old rats tends to be- 

 come roughened. This is conspicuously so at 726 days, and 



