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Universitj/ of California Publications in Zoology 



[Vol. 21 



that the interparietal in C deveh)ps from two and possibly three 

 centers of ossification. Tracts less densely ossified than the main body 

 of the bone divide it into three parts. It will be seen from figure 25 

 that a considerable area of cartilage extends back- 

 ward from the anterior border of the interparietal 

 in Z). This area of cartilage is seen to be somewhat 

 smaller in E (see fig. 5). As in the case of the 

 supraoccipital these conditions indicate that pos- 

 sibly more than one center of ossification is in- 

 volved. However, careful search among specimens 

 younger than Z> fails to reveal more than one center. 

 Ossification appears to proceed from one point and to result at first in a 

 crescent-shaped interparietal. The parietals and supraoccipital sur- 

 round the interparietal. It meets the supraoccipital squarely and with 

 the formation of the lambdoidal crest comes to have its posterior 

 margin recurved. The parietals are overlapped by the inter])arietar. 

 No trace of a suture between the parietals and interparietal can be 

 made out in skulls older than K. In L a sagittal crest is present. The 

 skulls of varying ages show that this crest develops first on the inter- 

 parietal. In that part of the interparietal on which the sagittal crest 

 develops sinuses also develop. Table 3 is significant in two respects. 



Fig. 25. Showiug 

 uiiossified area ex- 

 tending posteriorly 

 into interparietal 

 of D. X 21/2. 



I 



TABLE 3 



Showing Length and Width, in Millimeters, of Interparietal Bone in 

 Skulls of Different Ages 



When the measurements of the interparietal are compared with the 

 measurements given in table 2 of the other elements comprising the 

 dorsal surface of the skull it will be seen that the interparietal is rela- 

 tively much larger in the first than in the last of the series. The peak of 

 its development with respect to actual size is reached in F. After this 

 there is an actual decrease both in width and in length. K, it will at 

 once be noted, forms the single exception to this statement in that here 

 the interparietal is 12 mm. wide. Comparison with other skulls of 

 similar age .shows that in K the interparietal is a wide departure from 

 average conditions. In K two narrow lateral extensions have pushed 

 outward between the supraoccijntal and ]>arietals and increase the 



