6 PROCEEDINGS OF THE NATIONAL MUSEUM vol. CT 



The exposure of the frontals on the vertex of the skull appears to 

 be restricted to the protuberance behind the nasal passages. Pos- 

 terially the frontals abut against a narrow strip of bone which has 

 been referred to as the "interparietal" and anteriorly they are 

 sheathed by the nasals. The protuberance separates the posterior 

 extremities of the maxillae on the vertex of the skull. Laterally the 

 frontals are overspread by the ascending processes of the premaxillae 

 and by the horizontally expanded plates of the maxillae. At a lower 

 level, a thin plate of the frontal projects laterally, forming the roof of 

 the temporal fossa and in front of this each frontal sends out a large 

 supraorbital process which contributes a complete osseous loof for 

 the orbit. 



The construction of the cresentic foramina below the nasal bones in 

 the skull of Zarhachis (pi. 2) proved very puzzling on first examination. 

 In order to obtain more explicit data on the relations of the bones 

 involved, it seemed advisable to make a comparative examination of 

 the skulls of as many genera of living toothed whales as were available 

 for study. In the course of this review skulls were found in various 

 stages of growth, and these have cleared up whatever uncertainties 

 may have existed in regard to the construction of this portion of the 

 brain case. The interpretations herewith given for the bones inclosing 

 the nasal passages have been confirmed by direct comparison with 

 disarticulated skulls of living dolphins. 



In a skull of a young Berardius hairdi (Cat. No. 14218, division of 

 mammals, U.S.N.M.) from Bering Island the presphenoid rests in the 

 trough of the vomer and the thin lateral walls of the vomer embrace 

 the lower half of this bone. Dorsally, there is a second platelike bone 

 coextensive with the nasal passage which fits into a groove on the 

 upper margin of the lateral wall of the vomer and sheathes the upper 

 half of the presphenoid. One of these platelike bones is present in 

 each nasal passage. These bones fulfill the requirements of the ect- 

 ethmoids. Posteriorly, each ectethmoid meets the corresponding 

 frontal edge to edge on the outer border of the frontal fontanelle. 

 In older individuals the dorsal margins of the anteriorly directed 

 ectethmoids meet on the mid line and fuse with a perpendicular plate 

 of bone which extends forward from the base of the nasals to a point 

 in front of the nasal passages, thus completely inclosing the pre- 

 sphenoid. The thin longitudinal perpendicular plate either represents 

 the mesethmoid or a dorsal prolongation of the combined ectethmoids. 

 With age, these lateral ectethmoids sheath the internal borders of 

 the frontals and extend upward on the posterior walls of the nasal 

 passages until they meet the anterior margins of the nasal bones from 

 below. Minute foramina are sometimes present in these bones in 

 some of the genera of living porpoises. 



