SKELETON 



91 



epi-, opisth-, and pterotic occur. There is but a single pterygoid, while basi-, 

 pre-, and alisphenoids are not ossified. The membrane bones in existing amphi- 

 bians have separated from the integument and have sunk to a deeper position 

 than in fishes, but in many stegocephals the presence of grooves for the lateral 

 line system woidd indicate a close connexion between skin and bones. In the 

 latter group the membrane bones are numerous, but in existing species they are 

 noticeably reduced. Except in stegocephals and the caecilians there are large 

 vacuities in both floor and roof of the skull. The lower jaw also has a reduced 

 number of bones, there being at most five, including the articulare and the 

 mento-Meckelian. 



The most primitive conditions occur in the stegocephals (fig. 92), where, as 

 the name indicates, the dorsal surface is covered, leaving only gaps for the eyes 

 and nostrils. In general the account of the skull given on p. 74 f will apply 



P 



Fig. 93. — Skull of Amblysloma punctatum, after Wiedersheim. /, frontal; mx, 

 maxillary; n, nasal; os, orbitosphenoid; ot, otic bones; p, parietal; prf, prefrontal; ps, 

 parasphenoid; pt, pterygoid; ptc, pterygoid cartilage; q, quadrate; sq, squamosal; st, 

 stapes; vp, vomeropalatine. 



to these forms, and so far as the dorsal surface is concerned little more needs to 

 be said, aside from the fact that the supratemporal is sometimes transversely 

 divided, that an interparietal foramen occurs (indicating the existence of a 

 parietal eye), that the bones called supraoccipital may be interparietal, and that 

 the sclerotics are common. The floor of the cranium is formed by a large para- 

 phenaeo, bordered in front by a pair of (usually toothed) palatines, in front of 

 whichr ie the vomers. Of the cartilaginous parts almost nothing is known; a 

 few, cadlrly larval forms, have well-developed branchial arches preserved. 



Of the GYMNOPraoNES (caecilians) the cartilage skull is known only in Ichthy- 

 ophis; its peculiarities are the reduced parachordals, an ethmoidal nasal septum, 

 a stapes, perforated as in mammals, and alisphenoid and trabecular cartilages 

 more distinct than in most amphibia. Most noticeable of the cartilage bones is 

 the ethmoid, while otics and exoccipitals are fused as are quadrate and pterygoid. 

 The membrane bones form a complete roof to the skull, recalling the stego- 

 cephals, but the number of bones is smaller, squamosal, supratemporal, jugal 



