298 
The preoperculum contains a mucous canal, and is developed 
around that structure similarly to the infraorbitals. The operculum 
and interoperculum are comparable to a branchiostegal ray, perhaps of 
the mandibular arch, and the uppermost ray of the hyoid arch has the 
exact relations of a suboperculum. 
The pharyngeal bones were not originally parts of the branchial 
arches, as is shown by their development, and by the fact that the ph. 
inferiora rest upon the fifth arch, while the ph. superiora are suppor- 
ted by the third and fourth. They arise independently by the fusion of 
the cement plates of the teeth, and coalesce secondarily with the bran- 
chial arches. They are the remains of the dermal denticles which lined 
the buccal and branchial cavities in ancestral forms ?. 
The anterior vertebrae are much modified, but being intimately 
connected with the auditory apparatus they will be described with it 
elsewhere. The haemal arches and processes of the last six vertebrae 
are much expanded for the support of the rays of the caudal fin, their 
bodies and neural arches having completely disappeared. The body 
of the last vertebra consists really of three coalesced centra, and from 
its extremity the dorsal ridges, found on all the centra, are continued 
back to protect the terminal filament of the notochord, forming the 
»Deckstücke«. 
The dorsal fin consists anteriorly of a broad horizontal plate, 
which supports the anterior fin rays. A small bone in front of this, 
preformed in cartilage, represents the first interspinal, the anterior 
part of the plate being the corresponding ray. The second ray is horse- 
shoe shaped, resting on the extremity of the second interspinal, over 
which it can slide so that its limbs come into apposition with the 
lateral ridges on the fourth spinous process, and prevent it from being 
depressed. The third ray, which is completely ossified, is attached to 
the second by ligament, so that when the latter is fixed, the former is 
necessarily so also. 
The pectoral arch consists of two portions, a large clavicular por- 
tion, consisting of a supraclavicula connected with the skull and a 
coalesced meso- and infra-clavicula meeting in the middle line with its 
fellow of the opposite side and being united to it by ligament; and a 
smaller posterior coraco-scapular portion, of which the two constituent 
parts are coalesced, and which also unites with its fellow of the oppo- 
site side, the union being in this case sutural. The anterior ray of the 
fin is capable of fixation, by means of a slightly curved ridge at its 
base, which, when the fin is erect, fits into a semi-circular groove on 
2 O. Hertwig, Zahnsystem der Amphibien. Arch. f. mier. Anat. Bd. XI. 
Suppl. 1874. Also Jen. Zeit. Bd. VIII. 1874. 
