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PROCEEDINOii OF TEE NATIONAL MUSEUM. 



VOL. 57. 



to the parietal for a considerable distance, and passes down behind 

 the eye cavity to join the ascending process of the postorbital process 

 of the jugal arch, with which it becomes continuous, and in old indi- 

 viduals firmly united by suture. The orbital cavity is thus completely 

 encircled by bone, by the completion of its posterior boundary. 



In studying a number of young skulls of the various species of 

 Tupaia and allied genera the postorbital process of the frontal is 

 found to be always separated from the frontal for a considerable 

 distance forwards, almost as far, in fact, as the supraorbital notch, 

 which in this group is converted into a foramen; and while I have 

 never seen it completely separated from the frontal, there is every 

 reason to believe, and I am fully convinced that younger specimens 

 will show, that it exists as a separate bone, ossifying from a separate 

 and distinct center. If this is true, then it follows that it is strictly 

 homologous with, and corresponds to, the element in this position 



/Pa 



Fig. 3.— TtJPAiA. Fr., frontal; /. Pa., interparietal: La., lachrymal; Mx., maxillary; Na., nasal; 

 Pa., parietal; Pmx., premaxillaey; Pr. F., prefrontal; Pst. F., postfrontal. x 2. 



in the skull of Rhynchocyon, just described. The temporal area is 

 somewhat larger than in RhyncJiocyon and is sharply delimited by the 

 diverging branches of the sagittal crest, which is very little developed 

 even in aged individuals. The share which the squamosal takes in 

 the formation of the outer wall of the brain case is smaU, and the 

 considerable exposure of the mastoid portion of the periotic upon the 

 postero-lateral aspect of the skull, rises weU above the squamo- 

 parietal suture. There is no paroccipital process. 



The jugal arch of Tupaia offers some points of unusual interest. 

 The most striking feature, at first glance, is the presence of a large 

 foramen, fenestra, or vacuity, piercing the arch below and shghtly 

 in advance of the postorbital process of the zygoma, as it rises up to 

 meet the corresponding process from above. Among the Insectivora 

 this vacuity is peculiar to Tupaia and the closely related genera, 

 in which it is usually very large and roomy, but is reduced to a small 



