SKULL — AMPHIBIA 



129 



extends behind its articulation with the quadrate. There are four gill-arches, 

 persisting as cartilage in the adult, while the copula extends forwards as a sort 

 of entoglossum. 



The adult skull has few cartilage bones. Exoccipitals and prootics 

 soon fuse with each other and with the large parasphenoid, forming 

 a large basal bone which extends forwards on the ventral surface to 

 the vomers, while dorsally the occipito-petrosal part is visible at the 

 base of the skull. A characteristic is the ethmoid (lacking in Uro- 

 deles) apparently composed of ect- and mesethmoidal parts, the 

 mesethmoid appearing in some genera between the frontals, while 

 ectethmoid parts are visible on the palatal surface of Ichthyophis. 

 There are no otic or basal processes to the quadrate; articulare and 

 angulare are usually fused. 



Fig. 137.' — Skull of Siphonops annulaius (Wiedersheim, '79). an, angulare; b, 

 basale; e, 'ethmoid;' /, frontal; m, maxilla; np, naso-premaxilla; p, parietal; pi, pala- 

 tine; po, petroso-occipital; q, quadrate; sq, squamosal; v, vomer. 



The homologies of some membrane bones are uncertain. Parie- 

 tals, frontals, nasals and premaxillas need no mention further than to 

 say that the latter two fuse in Siphonops. In or near the anterior 

 margin of the very small orbit is a prefrontal and adjacent to this a 

 small septomaxillary (called turbinal and lateral nasal) is visible in 

 some from above; it may fuse with the nasal. The suspensor of 

 the lower jaw is probably quadrate and squamosal, the latter on the 

 dorsal side. Between it and the maxilla the margin of the cranium 

 is formed by a membrane bone (fig. 138, pf), called jugal, zygomatic 

 and squamosal, but which development suggests is a postfrontal. 

 In the maxilla, or between it and the premaxilla, is the foramen for 

 the tentacular apparatus characteristic of the order. Ichthyophis has 

 a small bone above the orbit, probably a supraorbital. 



The large basale on the ventral surface has been mentioned. 

 Palatine and maxilla fuse, both elements bearing teeth as does the 



