62 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
The cerato-hyoideus interims , a smaller and more slender muscle, 
arises from the postero-ventral border of the proximal end of the 
hyoid and, widening, inserts on the postero-ventral surface of the 
proximal end of the first epibrancliial. 
The thoracico-hyoideus consists of two long and rather thick 
muscles, the stern o-hyoideus and the omo-Ziyoideus. I was unable 
to find their origin, but from analogy with Proteus and Necturus, I 
should expect it to be with the origin of the rectus abdominis on 
the posterior border of the first cerato-branchial. Both muscles lie 
ventral to the rectus abdominis and are almost contiguous to it 
anteriorly. Posteriorly they diverge from it and from each other, 
inserting separately, the sterno-hyoideus on the inner surface of the 
shoulder girdle between the procoracoid and the coracoid, the omo- 
hyoideus with the trapezius on the inner surface of the girdle between 
the procoracoid and the scapula. 
The two interbranchiales (the subcerato-branchiales of Driiner), 
are slender, very short muscles, parallel to each other. The first has 
two heads, (a) and (b) ; (a) arises from the proximal end of the 
first epibrancliial at its antero-ventral border, distal to the cerato- 
hyoideus internus, thus traversing the entire width of the cartilage, 
and passes dorsal to the adductor arcus tertii; (b) has a similar 
origin, distal to (a), and passes ventral to adductor arcus tertii, 
inserting with (a) on the postero-ventral surface at the proximal 
end of the third epibrancliial. The second interbranchial takes its 
origin from the antero-ventral surface at the proximal end of the 
second epibrancliial and inserts near the first interbranchial, distal 
to portion (b). 
The two adductores arcuum are short, slender muscles associated 
with the second and third gill arches; that of the second gill arch 
arises from the first myocomma of the rectus abdominis and inserts 
on the ventral surface of the second epibrancliial at its proximal 
end; that of the third gill arch arises from the second myocomma 
of the rectus abdominis and inserts on the ventral surface of the 
third epibrancliial at its proximal end. 
The remaining hyoid muscles are best seen from a dorsal aspect. 
The levatores arcuum serve to raise the gill arches, and are five 
in number. The first is short and thick, arising from the temporal 
region of the skull jiosterior to the first head of the digastric. It is 
covered distally by the cerato-hyoideus externus and inserts at the 
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