No. 3.]} MUSCLES AND NERVES IN AMIA CALVA. 705 
The course and position of all these nerves indicate that the 
skull in its posterior portion, as in its anterior portion, develops 
more rapidly than the inclosed brain, and that posterior to 
some central point, approximately the nervus acusticus, the 
issuing nerves are, by that development, pulled or pushed 
backward, just as in front of that point they are pulled forward. 
The glossopharyngeus is an exception to this rule, for it runs 
almost directly outward through the auditory cavity instead of 
behind it. The auditory vesicle, which ‘develops between the 
facial and glossopharyngeal nerve roots’’ (No. 4, p. 232), seems, 
in fact, as it developed, to have invaded and occupied the 
glossopharyngeal region of the head, and, in so doing, to have 
pushed the vagus and lateral nerves before it, but to have left 
the glossopharyngeus in its natural position, the sinus utriculi 
posterior pushing backward above that nerve, and the sacculus 
below it. In the tadpole, the glossopharyngeus is apparently 
not treated with similar consideration, for Strong shows it 
lying, with the vagus, posterior to the auditory capsule. 
The brain, in the adult Amia, does not lie on the floor of the 
occipital chamber; on the contrary, it traverses the chamber 
at such a height that about one fourth the chamber lies below 
its ventral surface. The extreme posterior end of this ventral 
portion of the chamber ends (Fig. 11, Pl. X XI) in a blunt point 
in the line of the center of the vertebral column, and hence, of 
the center of the notochord. This part of the chamber lies 
on a level with the main portion of the eye-muscle canal, and, 
like that canal, is developed in late larval or postlarval stages. 
It is filled, in the adult, with fatty tissue. 
In the walls of the occipital chamber there are three large 
ossifications, which extend from the outer to the inner surface 
of the skull. They are the two occipitale laterale, the exoccip- 
itals of Bridge, one on each side of the head, and the median 
basioccipital. 
The basioccipital (BO, Figs. 8-11, Pl. XXI) is described by 
Sagemehl as having the shape of a muscle-shell. It is a stout 
bone, has approximately the length of the first six vertebrae, 
and its posterior third is solid and shaped like a vertebra 
(Sagemehl). Both ends of this solid portion are concave, and 
