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A small cavity exists between the prootic and the parasphenoid, 
representing the almost aborted canal for the orbital muscles. Another 
cavity exists in the upper table of the pterotic (squamosal), extending 
into the supraoccipital and epiotic. It is quite shut off from the cra- 
nial cavity, and opens by a small foramen behind, seeming to be the re- 
presentative of the »temporal cavity« described by Sagemehl! in 
Amia. 
In a young stage, wherever a mucous canal occurred in transverse 
section, a ring of bone surrounded it. This protecting osseous tube is 
at first distinct from the subjacent bone, but eventually unites with it. 
The bones of the infraorbital chain, the nasals, and the adnasals, are 
formed by the growth of this osseous tube. The frontals are formed by 
its fusion with subjacent membrane bone, and the sphenotic (postfron- 
tal) and pterotic by its union with the subjacent perichondral bone. 
The basioccipital is hollowed out about the middle of its length for the 
sacculus, and in younger stages this excavation has extended so far as 
to leave no cartilage in this region, but only a thin plate of bone con- 
tinuous with the perichondral layer of the exoccipital. In an older 
stage however cartilage is present, having grown forwards from the 
| unexcavated portion, so that there is relatively more cartilage in the 
older than in the younger stage. At first the auditory apparatus is 
very large, but later it does not grow as rapidly as do the cranial walls, 
and thus opportunity is given for the forward growth of the cartilage. 
Only one pterygoid — ‚the metapterygoid is present. Another 
bone (absent in A. nigricans) occurs between this and the palatine, but 
since it is not preformed in cartilage, but is an ossification of the fascia 
covering the M. add. arcus palatini, it cannot be placed in the 
category of pterygoid bones. The maxilla is modified into a support 
for the long maxillary tentacle, and bears no teeth, nor does it show 
any traces of any in its development. So also with the Vomer. The 
intermaxillary is very large and toothed. The dentary of the man- 
dible on its upper surface is formed by the fusion of the cement-plates 
of the teeth, at the sides by perichondral bone, and below by mucous 
canal bone, all of which are histologically identical and pass without 
any limitation into one another. 
The hyomandibular projects far forwards, pushing in front of it 
the metapterygoid, this anterior projection being for the protection of 
the R. hyoideo-mandibularis facialis, and is formed in mem- 
brane. The symplectic remains unossified. 
1 Morphol. Jahrb. Bd. IX. Hft. 2. 1883. 
