THE ENTIEE SKULL 



501 



FIG. 403. 



petro-mastoid is complete. The tentorial process of the parietals has 

 assumed its adult proportions. 



The anterior lateral fontanelle has disappeared, as has also the 

 posterior part of the pterygo-alisphenoidal suture. The orbital wall 

 is completely ossified. The frontal 

 sinus is still rudimentary; the sphe- 

 noidal sinuses are well developed and 

 contain the lowest ethmoidal scrolls. 



The lateral ethmoid has reached 

 its adult form ; it does not cover the 

 maxillo-turbinal, however, and the 

 scrolls are less complicated. The 

 fourth piece is still joined to the 

 cribriform plate by cartilage. The 

 cribriform plate has ossified, and a 

 bony strip, two millimetres in width, 

 appears in the posterior end of the 

 mesethmoid. With the exception of 

 the small first upper molars, all the 

 milk teeth are in place. 



The skull at thirty-five days 

 does not differ noticeably from the 

 preceding skull ; the ectotympanic 

 has joined the squamous. 



The skull at forty-four days (Fig. 404) does not differ in a 

 marked degree from the skull at thirty days. The interparietal is 

 much smaller ; the posterior part of the petro-mastoid is larger ; the 

 external auditory meatus is reduced by the increased width of the 

 ectotympanic ; the entotympanic is more strongly ossified and is joined 

 more closely to the ectotympanic. 



There are now no fontanelles, and there is merely a trace of the 

 anterior end of the pterygo-alisphenoidal suture. The postorbital 

 processes are larger. The frontal sinuses are well developed. 



The scrolls of the lateral ethmoid are joined by bone to the 

 cribriform plate ; the lower scrolls are more distinctly subdivided and 

 cover a larger part of the maxillo-turbinal. The diameter of the bony 

 mesethmoid, measured at right angles to the cribriform plate, has now 

 reached three millimetres. 



THE SKULL, THIRTY DAYS AFTER BIRTH. 



(Natural size.) 



