8 PROCEEDINGS OF THE NATIONAL MUSEUM vol.67 



Grampus skull, the dorsal margins of the lateral platelike bones or 

 ectethmoids do not meet above the presphenoid as in an older in- 

 dividual and above the level of the latter there is a fissure which 

 extends inward from the internal margin of each ectethmoid to the 

 rudimentary foramen for the nerve. In addition to this fissure, there 

 is a shallow groove leading upward from the foram.en and passing 

 obliquely across the upper extremity of the ectethmoid. The 

 ectethmoid has enveloped the foramen. In other mammals, the 

 nasal branch of the ophthalmic division of the fifth cranial nerve 

 passes outward on each side of the mesethm^oid betw^een the latter 

 and the ectethmoid. 



A critical examination of the Zarhachis skull (pi. 2) shows that the 

 ectethmoid in the region of the crescentic foramen is more noticeably 

 modified than is the case in the skull of the young Grampus. As in 

 the latter, a fissure extends inward fromi the internal margin of the 

 ectethmoid to the foramen, but the whole bone is more or less in- 

 voluted. Each ectethmoid in the region of these crescentic orifices 

 is twisted almost at right angles to the main body of the bone. The 

 curvature of the ectethmoid around the foramen is so unusual in 

 appearance that one might view the semiovoidal rostral border or 

 the margin which is visible on plate 2 as being actually the outer 

 margin of the ectethmoid, and the that border which surrounds the 

 foramen at the bottom or at the caudal end of the deep crescentic 

 aperture is the internal margin. If this is the true explanation, then 

 the flattened condition of the ectethmoid in living porpoises is a later 

 development and is indicative of one of the methods by which the 

 closure of the foramen has been effected, with the accompanying loss 

 of the sense of smell. It should also be noted that the thin per- 

 pendicular plate extending from the nasals to a point in front of the 

 nasal passages has been destroyed. 



The dorsal border of the anterior wall of each nasal passage is very 

 thin and projects dorsally for 15 mm. or more above the porous plug- 

 like portion of the presphenoid. Although a number of genera of 

 toothed whales were studied, no skulls were found in which the 

 construction of the nasal passages corresponded to the Zarhachis type 

 of architecture. In Phocaena (Cat. No. 3659), Tursiops (Cat. No. 

 22299), and Lipotes (Cat. No. 218293), the dorsal margin of the 

 anterior wall of each nasal passage is formed by a portion of the 

 internal border of the maxilla. In all the toothed whales examined, 

 the maxilla contributes part of the anterior wall of the nasal passage 

 and, with the exception of Inia and Stenodelphis, it always constitutes 

 the upper border of the anterior wall. In Inia and Stenodelphis, 

 however, the premaxillae are thickened dorso-ventrally and closely 

 approximated at the base of the mesorostral gutter; they constitute 

 the upper border of the nasal passages. In Zarhachis, however, at 



