400 University of California Publications in Zoology [Vol. 2] 



growth in different parts of the skull and showing the time at which 

 this growth occurs, will prove more valuable in the present state of 

 knowledge than lengthy discussion. The means selected to present 

 these data are : illustrations, and measurements from which ratios and 

 percentages have been and may be further computed. 



In Review 



The following points concerning the ontogeny of OtospennopJiiJus 

 gramnuirus beecheyi are believed to be of most general morphologic 

 interest : 



1. There is an actual decrease in the postorbital breadth with 

 increase in age. 



2. The interparietal undergoes an actual decrease in width and in 

 length with increase in age. 



3. A separate center of ossification for the part of the frontal that 

 lies immediately anterior to the region later occupied by the orbito- 

 sphenoid is shown in a stage shortly before birth. 



4. The center of ossification in the basisphenoid and the center of 

 ossification in the presphenoid are separate and di-stinct from one 

 another and from the centers of ossification in the ali- and orbito- 

 sphenoids. Each alisphenoid and each orbitosphenoid also has a 

 separate center of ossification. 



5. Shortly before birth the tympanic spreads both anteriorly and 

 i)osteriorly along Meckel's cartilage from the point of union of 

 Meckel's cartilage and the anterior end of the tympanic. 



6. The incus assumes the same shape that it has in the adult at a 

 time when the shape of both the malleus and stapes is still quite unlike 

 that seen in the adult. The head of the malleus ossifies before any 

 other part of the malleus or any part of either the stapes or incus 

 does so. 



7. The petrosal shows an early fusion of the squamosal and petrous 

 portions. A cup-shaped depression for the reception of the posterior 

 end of Meckel's cartilage develops in the squamosal portion of the 

 petrosal. 



8. A post-hypophyseal bar grows out from each petrosal and 

 unites with its fellow across the floor of the brain case. 



9. Milk Pm- is less molariform, but more complex, than the per- 

 manent Pm*. 



