246 THE VOYAGE OF H.M.S. CHALLENGER, 



articulatory excavation which is enlarged by a smaller depression on each side ; the 

 suture between this bone and the upper occipital is distinct, but the paroccipitals seem 

 to have coalesced with the supraoccipital (spo). The latter bone penetrates between, but 

 does not entirely separate the parietals (p). The bones on the side of the cranium are 

 coalesced. The basale (figs. 10, 12, b) has a singular shape ; it is dilated into a pair of 

 lateral wings closing part of the side of the cranium, and separated from the frontal by 

 the intercalated alisphenoid (po) ; at the base of the skull it forms the pair of strong 

 ridges already mentioned, convergent anteriorly, where the bone is narrowed into a 

 styliform slightly curved process which supports the membranous interorbital septum, 

 and extends forwards to the rostral process. The frontals (figs. 10, 11, /) are very 

 narrow, especially above the orbit, and taper into fine points in front. The ethmoidale 

 medium (em) is a narrow long single bone situated above the remains of the ethmoidal 

 cartilage (ec). 



The foremost part of the snout (figs. 10, 15) is formed by a cartilage, the lower 

 part of which is ossified, whilst the upper projects free as a flexible rostral appendage 

 (/). The ossified portion (?•) is wedged in between the ascending processes of the 

 intermaxillary, which are firmly attached to it, so that this latter bone is not capable of 

 being moved in any direction. It almost entirely excludes the maxillary (m) from the 

 margin of the jaw. The maxillary is fu-mly tied to the intermaxillary, and therefore 

 also not capable of free motion ; its distal extremity is bifid, the lower end being bent 

 downwards beyond the extremity of the intermaxillary, and the upper modified into 

 an acute spine. 



A singular nodule of cartilage (fig. 10, n) which has no direct connection with the 

 rostral cartilage, and can be moved independently, is lodged in the fibrous tissue filling the 

 angle between the intermaxillary and basale. 



Of the suspensorium the hyomandibulare (fig. 13, km) is the largest bone ; in 

 fact it is of unusual size, subtriangular, narrowest below, and provided with a raised 

 strong, obtuse ridge. Three bones are joined to its lower edge, the entopterygoid (cjj), 

 the symplectic [sy), which is almost entirely cartilaginous, and the stylohyal (st). The 

 quadrate (q) is narrow, produced to a point in front of and Ijehind the mandibulary 

 joint, and forming a long suture with the ectopterygoid (ecj)). A rather lai'ge vacuity 

 exists between the quadrate and entopterygoid. 



The ectopterygoid (ecp) extends forwards nearly to the end of the pal ato -pterygoid 

 arch, has a subvertical position, and is provided above, near its anterior end, with a pair 

 of small protuberances for the attachment of ligaments and muscles. To its lower edge 

 are attached rather loosely the palatal bones (paZ) which together form an arch joining 

 in the median line, and which are armed with a series of teeth like the jaws. There is 

 no vomer. 



The palatal series of teeth is opposed to that of the lower jaw, as in sharks ; and 



