234 THE VOYAGE OF H.M.S. CHALLENGER. 



extends upwards towards the paroccipital, from which it is separated by a linear strip of 

 cartilage. The articular facet (a) for the hyomandibular extends a long way above the 

 alisjihenoid and exoccipital immediately below the upper edge of the cranium. Finally 

 a small quadi-angular ossification (pt) occupies the postero-lateral corner of the brain- 

 capsule ; it is so thin that it can be easily pressed into the ear-cavity ; perhaps Parker's 

 name pterotic may be applied to it. 



The base of the skull is occupied, as usual, by the very large basale (6). 

 The membrane bones on the upper surface ofi'er the peculiarity that the parietals 

 (fig. Z,p) are joined by a long median suture, and not separated by a process of the 

 supra-occipital ; they are bordered on each side by a squamosal [sq) oblong in form. 

 The frontals (/) are large and long, each longitudinally divided by a groove into a median 

 and supraocular portion. The narrow part of the snout is occupied by a long unpaired 

 bone, the ethmoidale medmm (em), which in front is expanded into a short lateral process 

 (fig. 4, em'). This process is folded downwards to the lower side of the snout, where it 

 forms on each side a semicylindrical groove (fig. 6, e) for the reception of a nerve 

 (olfactory ?) and blood-vessels. The two canals are separated by a narrow bony promin- 

 ence, on each side of which there is a foramen for the passage of the nerve. There lie 

 on each side of the median ethmoid two dermal bones, connected with it only by the 

 intervening skin ; they are two nasalia, of which the posterior (fig. 3, n) is oblong in 

 shape, and the anterior (an) linear with a very thin lobe in the middle. 



The lower side of the snout is covered by the long vomer (figs. 5, 6, v) longitudinall}^ 

 hollowed out, and bordered in front by a high horse-shoe-shaped ridge which docs not 

 bear any teeth. It is suturally connected with the basale, but touches only partly the 

 ethmoidale medium, part of the ethmoidal cartilage being unprotected by bone on the 

 side of the snout. 



The terminal rostrale (r) with the termination of the ethmoid cartilage (ec) has been 

 mentioned above. 



The palato-quadrate arch (fig. 2) also represents peculiarities in the absence or 

 rudimentary condition of some of its component parts. 



The hyomandibulare {hm) is a subquadi-angular lamella with a deep groove and wide 

 foramen in its anterior half; its greater portion is cartilage, which, however, is entirely 

 covered with an ossified superficial stratum. It is joined to the cranium by the whole 

 leno^th of the upper side of the quadrangle ; the angle between the two posterior sides 

 olTers the base for the articulation of the operculum ; the lower angle is slightly produced 

 downwards, and has the thin styliform cartilaginous symplectic (sy) attached to it. Its 

 anterior side is partly free, partly suturally connected with the metapterygoid. 



The metapterygoid {mp) is a fan-like bone with the angle of the fan directed back- 

 wards and overlapping the lower corner of the hyomandibulare ; one half of its convexity 

 forms a connection with the quadrate, the other half with the entopterygoid (ep). 



