No: 30) MWUSCEES, AND NERVES [IN AMIA CALVA. 703 
the first cervical nerve and the vagus. By these definitions 
that part of the skull that lies between the glossopharyngeal 
and vagus foramen, in the adult, and the glossopharyngeal 
somite or segment of the head, in embryos, are definitely 
excluded from the region. In selachian embryos the glosso- 
pharyngeal somite is similarly excluded from the occipital 
region of the head by van Wijhe (No. 130), Kaestner (No. 62), 
Killian (No. 63), and others, Hoffmann (No. 57) even excluding 
with it the first vagus somite. Sagemehl (No. 104, p. 189), in 
opposition to these views, defines the occipital region of the 
skull, in Amia and in all bony ganoids and teleosts, as that 
part of the skull that lies posterior to the glossopharyngeal 
foramen and to the hind edge of the petrosal, the reason 
given for this definition being that, in some rare instances in 
teleosts, the glossopharyngeus and vagus issue through the 
same foramen. Mollier (No. 82), in embryos of reptiles, gives 
practically the same definition as Sagemehl, for he takes the 
hind edge of the auditory vesicle, which lies immediately in 
front of the giossopharyngeus, as the anterior limit of the 
occipital region of the skull. Froriep, in a recent work on 
embryos of mammals, birds, and reptiles (No. 35, p. 575) 
apparently assigns the same anterior limit to the region, though 
he does not definitely so state. This latter definition differs, 
therefore, from his earlier one. According to it, and to the 
definitions of Mollier and Sagemehl, the glossopharyngeal 
somite must either be absorbed by the auditory vesicle or be 
included in the occipital somites of the head. In either case, 
occipital and postauditory would be, in the adult, synonymous 
terms, and as such I consider them in Amia in all stages 
included in this investigation. 
In the interior of the skull of the adult Amia, there is a 
large postauditory portion, or chamber, occupying almost one 
third the length of the cavum cranii. This chamber is sepa- 
rated from the labyrinth recess by a ridge of cartilage which 
projects, in a curved line, forward and inward from the inner 
surface of the lateral wall of the skull. This ridge of cartilage 
is, in young larvae, the bulging hind wall of the auditory cap- 
sule and of the skull, for, as will be later shown, that part of 
