22 CLASS XIV. 



(tinea later alls] for secreting mucus, as its continuation on to the 

 head 1 . The anterior of these sub-orbital bones, which is also the 

 largest, forms the outer or inferior margin of the nasal cavity. 

 The superior margin of the sac of the olfactory organ is formed by 

 a small plate of bone (the nasal bone according to CUVIER), which 

 also appears to belong to the dermal skeleton, and runs on each 

 side of the anterior frontal bone to the bone of the upper jaw. It is 

 the turbinated bone according to OWEN. 



The under jaw is divided into a right and left portion ; these 

 two halves are united in the middle by cartilage and ligamentous 

 tissue alone. Each half usually consists of three pieces ; an ar- 

 ticular piece on each side (os articular e), beneath it a small bony 

 piece for the angle of the lower jaw (os angular e], and an anterior 

 piece, in which the teeth are fixed (the dental piece, os dentale), in 

 the posterior margin of which is a triangular excisure for the recep- 

 tion of the articular piece. 



We must next consider the tongue-bone, which presents a large 

 development in the class of fishes, from its connexion with the gills, 

 as an osseous respiratory apparatus. The body of the lingual bone 

 lies under the head in the mid-plane, and usually consists of a 

 series of unpaired bony pieces placed behind one another; forward, a 

 cartilaginous or bony lamina penetrates into the tongue (glossoJiyale 

 GEOFFROY SAINT-HILAIRE). To these bony pieces five arches are 

 attached, like ribs to a sternum. The hindmost arc is incomplete, 

 and is simply laid on the under side of the gullet ; it consists on 

 each side of a bone, which, on its upper surface, almost always bears 

 teeth (the so-named ossa pharyngealia inferiora}. In some fishes 

 (Scarus, Labrus] the two unite to form a single unpaired bone. 

 The four anterior arches consist of several bony pieces, of which the 

 uppermost mount up beneath the skull and bear teeth on their 

 inferior surface (ossa pharyngealia superiora) ; the two middlemost, 

 which are grooved beneath, bear the branchial laminae. At the 

 side, and in front of the first branchial arch, two small bones are 

 situated on each side, to which the horns of the tongue-bone are 



1 Compare STANNIUS Ueber die Knochen des Seitenkanah der Fische, FKOKIEP'S 

 Neue Notizen, Bd. xxui. s. 97 100 (April, 1842). Of the same kind are certain bony 

 plates, which in many fishes are situated laterally near the parietal bones, the os 

 supra-temporalia of BAKKEB and CUVIER. 



