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primitive features, yet in other respects remind one more of the 

 Amniotes. This holds e.^. for the earliest stages of development of 

 the egg, which are nearly identical in Petromyzon and Urodelans» 

 and also for the origin of the hypophysis in front of the mouth involution 

 (in Selachians and Amniotes from the roof of the latter), for the 

 structure of the brain which still lacks a developed metencephalon 

 in Petromyzon and Amphibians, for the presence of horny teeth 

 round the mouth (in Amphibians at least in the larval stage) and 

 for the development of the cranial muscles (Edgkworth, 191 J, 

 p. 292). It holds equally for the backward extension of the skull. 

 Into the last the first three post-otic somites have now been in- 

 corporated, together with the first free neural arch of Petromyzon 

 which in ontogeny appears as the so-called occipital arch, bounding 

 behind the foramen vagi (Stöhr, 1879, 1881). The occipital 

 region of Amphibians accordingly contains only one vertebral 

 rudiment (Skwertzoff, 1897, p. 262). Between the occipital arch 

 and the auditory capsule in early ontogeny three somites can be 

 recognized (Miss Platt, 1897, p. 448, for zV^c^n^.?, Sewertzoef 1897, 

 p. 260, for Pelobate.'i, possibly also for Sirtdon, cf Platt, 1898, 

 p. 450) the last of which lies over the space between the 4'^'i and 

 the 5"' gill-slit (Miss Platt, 1897, Marcus for Gymnophiones, 

 1910). These three are the somites of the glossopharyngeus, of the 

 primary vagus, and of the first spinal ganglion which fuses with 

 the latter ("spinalartiger Vagusanhang", Hatschek, 1892, p. 158). 

 Of this fusion indications were observed in ontogeny by Miss Platt, 

 (1897, p. 448) and Marcus, (1910, p. 378). To the last head-segment in 

 young stages a ventral root, a so-called occipital nerve (Fürbringer, 

 1897, p. 353), was observed in a few cases (Fürbringer, 1897, p. 

 486, Peter, 1898, p. 42, Drüner, 1901, 1904, Osawa, 1902, Marcus, 

 1910, p. 376) which, however, during further development disappears. 

 Of the three post-otic somites only the posteriormost in Urodelans and 

 Gymnophiones still produces a regular myotome, which gives rise 

 to the anterior segment of the longitudinal trunk mnsculature and, 

 like the 3^' post-otic myotome of Petromyzon, is inserted at the auditory 

 capsule. Both the anterior post-otic myotomes, the deeper parts of which 

 already in Petromyzon showed reduction, have been snppressed, 

 evidently by the extension of the auditory capsule; only the second 

 may still produce a few muscle fibres (Miss Platt, 1897, \^. 447, 

 Marcus, 1910, p. 430). In phaneroglossan Anurans, however, the 

 3^ and the 4^'^ post-otic myotome (Sewkrtzoff, 1895, p. 269) also 

 disappear, together with the ventral root of the latter two, being 

 that of the first free spinal nerve. 



