316 



4 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



FiQ. 4. — Left lateral view of mandible of M. salmoides. Natural size, b}- the author, 

 from hia own dissections, tho various bones having been pulled apart to show their 

 entire shape. D, dentary; m.u., Meckel's cartilage; -i?-i., articular; Ang. , ansnlar. 



again, iu the middle line, the somewhat small subcircular foramen magnum, inclined 

 to be subcordate in outline in some specimens. Often iu the common cod, always in old 

 individuals, I believef 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 prasmaxillary and its 

 fellow in front bearing 

 the teeth (Pma;,) (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, talceii 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 interhyal, 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 branchiostegal rays (fig. 3, Bs. 

 B.) constitute the skeleton of an organ of 

 defense to the respiratory apparatus, and that many believe that the opercular bones 

 are merely modified branchiostegal 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 the upper jaw of M. 

 saltrKyides, together with the 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; 

 Ptnx, premaxillary; I'L, palatine; a, admaxillary. 



