316 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
again, in the middle line, the somewhat small subcircular foramen magnum, inclined 
to be subcordate in outline in some specimens. Often in the common cod, always in old 
individuals, I believe, this first or atlas vertebra fuses with the base of the cranium, 
and its long neural spine runs up nearly to the top of the supraoccipital crest, being in 
contact with the posterior margin of the same for the entire way. 
Apart from the cranium the chief features of the skull consist in the jaws, the upper 
one being formed by the maxillary [Mx.) on either side, and the prsemaxillary and its 
fellow in front bearing 
the teeth ( Pmx .) (fig. 3). 
These structures have 
been fully described in 
the Amia memoir, and 
the two figures there 
devoted to them are 
here reproduced as figs. 
3 and I. Attention is 
also invited to fig. 5, for 
that, taken in connec- 
tion with fig. 3 of the present paper, will clearly show the relations of another 
group of bones of the skull, namely, the opercular bones, or those of the gill-covers 
[Op., P. Op., S. Op., and I. Op.). Considerable attention has already been paid to 
these in the Amia contribution. In connection with them will be found the symplectic , 
a very interesting element in many bony fishes (fig. 3, Sym:). Then there are the 
bones of the suspensorium, connecting the cranium with the lower mandible (H. M., 
Sym., and Qu.). Of these, through the in- 
tervention of the inter hyal, the hyomandi- 
bular arch has also suspended from its lower 
extremity the hyoid arch, while its upper 
and posterior extremity also articulates with 
the operculum. 
Again, in the pterygopalatine arch of 
this bass we meet with the metapterygoid, 
the ento , and ectopterygoid and the palatine, 
and the relation of these bones to each other 
are shown in fig. 3 of the present paper and 
described in my Amia memoir, where also 
the hyoid and branchial arches of Micropterus 
have been touched upon in considerable 
detail. In this connection I have pointed 
out that the brauchiostegal rays (fig. 3, Bs. 
if.) constitute the skeleton of an organ of 
defense to the respiratory apparatus, and that many believe that the opercular bones 
are merely modified brauchiostegal rays. 
Passing from the skull and its arches we come to consider the shoulder girdle, a 
sequence of bones that have been differently viewed and differently named by different 
ichthyologists. In my work upon Amia calva I have contrasted in tables these various 
opinions and appellations, and figured the bones, and also named a bone, the supra- 
linear [si.), that is in a way connected with the shoulder girdle above (see fig. 3). 
Fig. 5. — The left outer aspect of tlie upper jaw of M. 
salmoides, together with t he hones associated with it. 
These latter are slightly dislodged from their normal 
positions, the better to show their relations. About 
two-thirds natural size, from the actual specimen, by the 
author, from his own dissections. Mx , maxillary; 
Pmx , premaxillary; PI., palatine; a, admaxillary. 
Fig. 4. —Left lateral view of mandible of M. salmoides. Natural size, by the author, 
from his own dissections, the various hones having been pulled apart to show their 
entire shape. D, dentary; m. c., Meckel's cartilage; Art., articular-, Any., angular. 
