ELASMOBRANCHS. 
10G3 
PISCES ELASMOBRANCHII. 
Fishes with cartilaginous endoskeleton (without dermoskeleton), with the shoulder-girdle 
detached from and suspended behind the head, with the maxillary (and mandibular) bones 
represented merely by loose cartilages at the sides of the palate and lower jaw, with the 
branchial arches entirely or partly united to the skin (gill-slits externally open or covered 
by a common dermal fold), and with diphycercal or heterocercal caudal fin. Fin-rays 
primary. Nostrils as a rule ventral". Air-bladder none. 
These fishes were removed from Artedi’s Clion- 
dr opterygii b by Bonaparte into a separate order, most 
clearly distinguished by the structure of the gills both 
from the preceding orders, which have borne the com- 
mon name of Tectobranchii 0 , as having the branchial 
cavity covered by a true opercular apparatus, belonging 
to the skeleton, and from the lower fishes, the Cyclo- 
stonii and Leptocardii, which are without true branchial 
arches. The union between these arches and the skin 
is accomplished in the Elasmobranchs by the extension 
of a membrane, supported by cartilaginous rods, be- 
tween the latter and each of the former. With this 
membrane too the several branchial lamellae- coalesce 
throughout their length. In some Elasmobranchs, in 
the suborder of the Chimaeras, however, the said mem- 
brane extends only in part, above and below, quite to 
the skin, a common branchial cavity being thus pro- 
duced on each side of the body. This cavity is fur- 
nished, as in the preceding fishes, with a single aper- 
ture, and the rest of it is covered by a dermal flap, 
extended on cartilaginous rods, which are homologous 
with the branchiostegal rays of the Teleosts, and by a. 
thin disk of cartilage (tig. 294, op), representing the 
operculum of the preceding fishes, but evidently form- 
ed here, as in the other suborder, by the mutual 
confluence of the upper (posterior) cartilaginous rods 
at the upper (anterior) end. Analogous cartilaginous 
rods also appear, as we have mentioned, in the mem- 
brane originating from each of the branchial arches, 
and supplying attachments for the branchial lamellau 
In the rest of the Elasmobranchs, the suborder of the 
Sharks and Rays, which is far superior in variety of 
form, the last-mentioned membrane, supported by its 
cartilaginous rods (figs. 298 and 300, rbr and br), is 
united throughout its extent, both from the hyoid and 
the branchial arches, either obliquely or in a straight 
outward direction, to the skin, which opens at the in- 
terstices into external gill-slits, numbering 7 — 5 in the 
surviving forms of this suborder. 
The scapular and pelvic arches are far more de- 
veloped in the Elasmobranchs than in the preceding 
fishes; and starting from the Elasmobranchs, morpho- 
a An exception is made by ancient (primitive) forms, such as Chlamydoselache anguineus , a Japanese fish remarkable in many other 
respects on account of its primitive characters, and described by G-akman, Bull. Mus. Comp. Zool. Harv. Coll., vol. XII, No. 1, and G-Onther, 
Deep Sea Fish., Chall. Exped., p. 2, pi. LXIV, LXV. 
b See above, p. 1043. 
c Hasse, Beitr. allgem. Stammesgesch. Wirbelth., Jena 1883, p. 12. 
Scandinavian Fishes. 
134 
