6 ALLIS. VoL. XII. 
1d 
is, from the tenth somite, or first trunk myotome of van Wijhe. 
The tenth somite of van Wijhe thus corresponds, in all these 
forms, in so far as its relations to the sternohyoideus are con- 
cerned, with the fifth muscle segment in Amia. In all these 
forms, also, the muscles of the pectoral fin in fishes, and 
of the neck and anterior extremity in reptiles, develop from 
myotomes posterior to van Wijhe’s tenth somite; that is, 
in Scyllium (Corning), from the sixth to the fourteenth 
myotomes ; in teleosts (Corning) and reptiles (Corning and 
Mollier), from the sixth to the thirteenth. In Scyllium the 
«‘Vornierenblaschen,” and in reptiles the ‘ Urniere,” begin at 
the sixth segment. The fifth intersegmental space in all these 
animals seems, therefore, to mark a definite limit, and this limit 
corresponds to the fifth intermuscular septum in Amia. The 
first muscle segment in Amia is therefore, in all probability, the 
sixth somite of van Wijhe, and there are, in Amia, the same 
number of head segments as in Acanthias (Hoffmann), that is, 
one more than in the head of Scyllium, of Pristiurus, and of 
reptiles. The one additional segment in Amia fuses with the 
hind end of the skull in post-larval stages. 
Opposite the sixth somite in Amia, as in Scyllium and 
Pristiurus (van Wijhe) and in teleosts (Harrison, quoted by 
Corning), lie the united vagus roots with no corresponding 
ventral root ; opposite each of the next two somites lies a ven- 
tral root, as in Scyllium and Pristiurus (van Wijhe) and Acan- 
thias (Hoffmann). Directly dorsal to these two ventral roots 
in Amia, there arise two distinct and separate roots of the 
vagus, in all probability the dorsal roots of the somites, and on 
these roots thereis part of an intracranial ganglion. Oppo- 
site these two somites in Scyllium and Pristiurus, van Wijhe, 
in his earlier work (No. 130), also found separate roots of the 
vagus. In later work he found a root opposite the seventh 
somite only (quoted by Rabl, No. 1o1, p. 118). In Acanthias, 
opposite the seventh somite, Hoffmann finds the posterior root 
of the vagus with a part of the vagus ganglion ; opposite the 
eighth somite he finds a rudimentary ganglion which soon dis- 
appears. Opposite the ninth somite, or fourth muscle segment, 
in Amia, there is a spinal nerve with dorsal and ventral roots, 

