754 ALLIS. [Vou. XII. 
43. The sternohyoideus is separated by two transverse inter- 
muscular septa into three portions. The posterior of these 
portions is innervated by a branch of the fourth occipital 
nerve, and thus belongs to the fifth and last occipital muscle 
segment, which is innervated by the same nerve. The two 
anterior portions of the muscle are innervated by branches of 
the united first, second, and third occipital nerves, and thus 
belongs to the fourth, and one or more anterior, occipital 
muscle segments. 
44. The development of the occipitale laterale indicates that 
that bone is formed of parts of three occipital dorsal arches. 
It is pierced by two ventral occipital nerves, and the nervus 
vagus issues along its anterior margin between it and the hind 
wall of the auditory capsule. It gives attachment to three inter- 
muscular septa. Posterior to it, on the dorsal surface of the 
basioccipital, there are two complete dorsal arches, each giving 
attachment to an intermuscular septum. In front of each of 
these two arches there is a complete spinal nerve with dorsal 
and ventral roots and dorsal ganglion. There are thus five 
vertebral segments indicated in the occipital region of the 
skull of Amia, the first, or most anterior, segment not being 
represented by a nerve, unless the vagus be, in part, that 
nerve. The posterior of these five segments fuses with the 
hind end of the skull in post-larval stages. 
45. A complete trunk vertebra, in larvae of Amia, contains 
six blocks of cartilage, three on each side. The dorsal block, 
on each side, is wholly independent of the other two, and is 
fused, in the adult, with the ventral end of the dorsal arch that 
lies next posterior to it in larval stages. The lateral block is, 
in larvae, connected at its anterior end with the posterior end 
of the ventral block. It bears at its outer end the rib. The 
ventral blocks lie on either side of the aorta, and resemble 
vertebral processes found in Calamoichthys and Salamandra, 
which, in those animals, are said to become the “ Basal- 
stiimpfe”’ of the haemal arches. If they be the homologues 
of those structures, as seems most probable, they are haema- 
pophyses, and the ribs of Amia may be true ribs, or pleuro- 
pophyses. 
