THE SKULL. 27 



These bones are narrower in R. esculenfa, and along the sagittal 

 suture are depressed into a groove : where the superior surface bends 

 down to become lateral the edg'es are much more prominent. In 

 11. teiiijioraria the bones are broader and flat or even somewhat arched. 

 The latter condition is still more marked in R. oxyrliinus. 



(5. The sphenethmoid, os etlnnouleiim (Figs. 10, 11, 14, and 



Cuvier, os en ceinture, I. c, p. 3S7, PL XXIV, a.— Dugès, n. 1 5.— Rathke, 

 anterior or sphenoidal wing (Vortr. z. vergL Anat. d. Wirbelthiere, 

 Leipzig, 1862, p. 42). — Meckel, Eiechbein, I.e., p. 502. — Parker 

 and Bettany, I. c, ethmoid. 



The long tubular cranium is completed anteriorly by a single 

 bone, which forms at once the roof, floor, and lateral walls. It is 

 consequently more or less ring-shaped, on which account it has been 

 named ' os en ceinture ' by Cuvier. Only the posterior portion is 

 annular, however : the anterior portion forms a double canal, with a 

 median partition, for the passage of the nerves of smell, and as these 

 canals are widened out anteriorly, this part of the bone helps to 

 complete the nasal cavities, which, however, are bounded for the 

 most part by cartilage, as described below. In some species of 

 frogs (as for example li. occellata, Rathke) this cartilage is partly 

 ossified. 



The sphenethmoid has on each side a small bony canal, ranning 

 forwards and inwards, through which the ramus nasalis of the first 

 division of the trigeminal nerve passes. 



The cartilaginous skeleton of the nose (Figs. 14 and j 6 n, %" , n" , 

 n""). The anterior borders of the funnel-shaped cavities of the sphen- 

 ethmoid pass into cartilage, which forms two capsules, separated from 

 each other by a median cartilaginous septum, and opening laterally. 

 We can distinguish, [a) a cartilaginous septum, forming a continu- 

 ation of the bony one ; [fj) the floor of the nasal cavity, narrower 

 behind, wider in front ; (c) a roof somewhat narrower than the floor. 

 The floor and roof are united in front by an arched surface. From 

 this cartilaginous capsule various processes project, which unite it to 

 other portions of the facial skeleton : firstly, from the most posterior 

 portion of the capsule there j)asses transversely outwards a bar of 

 cartilage {sn), which, widening, becomes continuous with the carti- 

 lage {s})") forming the basis of the anterior arm of the pterygoid 

 bone. From the anterior angle a cartilaginous process passes out- 

 wards (Figs. 14, 16 u"), which is attached to a projection on the 



