THE SKULL OF ACANTHIAS VULGARIS 423 



capsule, and on either side of the median keel is a fenestra or 

 fontanelle (the 'basal communication' of Gegenbaur) which 

 opens into the brain cavity a little behind the posterior margin 

 of the anterior fontanelle of the dorsal surface. 



In Acanthias each nasal capsule is almost spherical and is 

 composed of a very thin, easily broken cartilage. In this there 

 are thicker areas, which, at first sight seem to be separate car- 

 tilages, but which are really continuous with the rest of the 

 wall. The most marked of these regions is on the ventro- 

 medial part of the capsule, and at its postero-medial edge is a 

 small opening of the so-called 'ethmoid canal.' A second of 

 these denser areas is on the dorso-lateral surface and will be 

 described in connection with the lateral view. 



Immedialely surrounding the naris (ext.n.) is an elliptical 

 cartilage ring, a pointed cartilage bar extending across the short 

 axis of the ellipse from the anterior to the posterior side — con- 

 tinuous with the former, but free posteriorly. This supports 

 the flap of skin which divides the naris into its two functional 

 openings. 



Posterior to the nasal capsules a broad antorbital shelf (a.or.s.) 

 extends the width of the cranium and slopes postero-ventrally. 

 A continuation of the median rostral carina passes through this 

 as a slight median ridge. 



This shelf narrows abruptly so that between the orbits the 

 floor of the cranium has an almost tropibasic appearance, this 

 part, so far as can be judged from Sewertzoff's figures, being 

 developed from the trabecular plates, while the more dorsal 

 part of the orbital wall is derived from the alisphenoid cartilage, 

 the sphenolateral of Gaupp. This interorbital region is not of 

 the same width throughout; it narrows from the preorbital side, 

 then widens, and again constricts (this is the hypophysial re- 

 gion) and then widens again, passing, posteriorly, into the 

 broader basal plate of the interotic region. 



The more posterior of these constricted areas is the palato- 

 basal articular surface (p.b.a.) of Gegenbaur's description, which 

 is for articulation with the palatal process of the upper jaw. 

 Posterior to this surface the widened area extends farther ven- 



