964 
the greater part of the roof of the mouth, and 
likewise supporting all the formidab!e teeth with 
which this jaw is armed. Posteriorly it gives 
attachment to the inferior maxilla by two large 
articulating surfaces, and above it is only con- 
nected to the skull by the muscles implanted 
into it. From its upper margin it gives offa 
process, shown in the figure, which remains 
permanently cartilaginous, and in the living 
state is imbedded among the muscles that form 
the inner wall of the orbit; the whole is thus 
left completely moveable so as to give great 
latitude to the motions of the jaws. 
The superior maxillary bone (fig. 497, d) and 
the intermaxillary bone (c) are of very small 
size, being merely imbedded in the substance 
of the upper lip and connected superiorly b 
ligament to the face and the piece last described. 
Inferiorly these bones are attached to a third (fig. 
497, e, ) which is fixed by ligaments to the outer 
Fig. 497. 
i y m 
igs 
Inferior view of the skull, branchial arches, and pec- 
toral apparatus, of Squalus centrina. ( After Carus. ) 
a, nasal cavity; 6, wlfactory organ; ¢, superior 
labial or intermaxillary cartilage ; d, intermaxillary 
bones ; e, inferior portion extending between the 
preceding and the lower jaw; e, e, e, e, central 
sternum-like pieces ; /f. % FS, f, branchial arches ; 
i, i, iy branchial appendages; 4, scapular zone ; 
1, m, n, pectoral fins. 
PISCES. 
surface of the lower jaw at about one-fourth part 
of its length from the symphysis, so that the three 
together form an osseous and ligamentous hand 
that circumscribes the angle of the mouth and = 
materially diminishes the rictus of thejaws. The 
inferior piece (e) is most probably one of the 
elements belonging to the lower jaw d 
from its usual connections with that bone. - 
The inferior maxilla (fig. 497, 7) consists 
two lateral halves nie a Bi each 
half consists of a single piece of consid 
breadth, presenting a deep sulcus superiorly 
for the lodgement of the teeth. 
The branchial apparatus is placed further 
back than in the osseous Fishes, being situated 
beneath the commencement of the spine—a 
circumstance which causes the bones of the 
shoulder to recede backwards also. 
The whole of the opercular apparatus is 
wanting in the cnseibechana Fishes with the — 
exception of the Sturgeons ( Sturionide ), which 
seem in many respects to occupy an interme- 
diate place between them me the osseous 
division. { 
The os hyoides in Squatina and the Sharks — 
generally is com of three pieces, one 
situated in the mesial line, and two lateral — 
branches. The mesian piece or body of the 
os hyoides corresponds to the bones of osseous 
Fishes; while the large rami, i of 
mounting up to be connected with the sty- 
loid bones, terminate immediately ind | 
the articulation of the lower jaw, with which 
they are intimately conn by means of 
strong ligaments. From its posterior margin 
branchiostegous rays are given off precisely as 
in the former group, but these have nothing to 
do with the formation of an opercular flap, the 
branchial apertures being here of a very diffe 
rent character. a 
The branchial arches in their general arran ge 
ment resemble those of the osseous Fishes, b 
there are nevertheless important differences t 
beremarked. In Sguatina there exists inferiorly 
a kind of sternal apparatus which occupies th 
mesial line. This consists posteriorly of a cet 
tral piece (497, e, e, e,) that very nearly resemb 
a broad spear-head, forming a kind of sternut 
the handle of the spear closely representing t 
xiphoid cartilage of the human sternum ; @ 
in front of this are three pieces on each sit 
something like the costal cartilages. Of th 
the anterior pair are united to each other 
mesial line, while the second and third 
fixed to the sides of the central piece first-m 
tioned. The arches supporting the. b 
are five in number on each side, (fig. 497 
each consisting of an inferior and superior 
tion connected with each other by move: 
articulations. The inferior portion consists 
single piece, the superior of two, united tog 
by ligaments. The anterior arch is conm 
by ligaments to the body of the os hyoides 
also to the central pieces. The four posté 
are attached by ligament to the succeet 
lateral processes of the sternal apparatus, ‘ 
thus a framework is formed that almost entit 
surrounds the neck. The superior extrem 
of these arches are fixed beneath the ante 
4 
