No. 468] MUSCLES OF ACANTHIAS AND RAIA. 897 
tralconstrictors. This bridge extends about halfway from the 
end of the hyoid arch to the first gill slit. The remaining fibers 
pass over into those of the ventral constrictors, forming a con- 
tinuous muscle. The fibers follow the direction of the gill slit in 
their course. 
The remaining dorsal constrictors (three to six) are so closely 
similar that one description will serve for all (Fig. 2). The 
tendinous aponeuroses between them are somewhat curved, each 
ending at the top of a gill cleft and covering an underlying extra- 
branchial cartilage. The muscle fibers run nearly vertically and 
those attached to the aponeuroses are often also attached to the 
extrabranchials. Towards the dorsal margin some of the fibers 
converge to a tendon at the posterior edge of the muscle, and 
these tendons, after piercing the trapezius (Fig. 11, Csd 2-6), 
have their points of origin among the fibers of the dorsal longi- 
tudinal muscles, the last being also attached to the shoulder 
girdle. The more ventral fibers arise from the aponeurosis 
behind each muscle and are in part inserted on the aponeurosis 
in front, and in part continuous with the fibers of the ventral 
constrictors. 
Ventral Constrictors. — The ventral constrictors (Csv) do not 
differ markedly from the dorsals, and like them are six in num- 
ber. Here I am at variance with Vetter (’74, p. 416) who does 
not describe a first ventral constrictor for Acanthias, but begins 
with Csv 2. This is, however, clearly the first ventral constric- 
tor, while his Csv8 2is really the Csv 2, for if we compare ven- 
tral with dorsal sides, we find that the muscle in front of the 
spiracle which is inserted on the upper jaw is, as Raia shows, 
the first, while that upon the hyoid is the second dorsal con- 
strictor. Just so, upon the ventral side the muscle attached 
to the lower jaw should be designated Csv7, that upon the 
hyoid, Csv2. With this exception my account of the ventral 
constrictors agrees well with that of Vetter. 
On removing the skin and dissecting away the large amount 
of connective tissue upon the ventral side of the body (Fig. 1), 
we find immediately in front of the pectoral girdle, a pair of 
muscles, the coraco-arcuales communes (Cac) which, running 
forward, soon disappear under large sheets of muscle (Csv 7, ? 
