542 
CAPTAIN E. W. SH'ANN ON 
dorsal surface of the coraco-arcual septum, from just behind the fused trunk of the 
first and second afferent arteries to the level of the third afferent artery, is inserted 
on the inner border of the first hypobranchial and on the dorsal aspect of the basihyal. 
The c.br. of either side are in contact in the middle line from a very short distance 
behind their insertions to their origins on the sdptum. I agree with Vetter, who 
observed a similar condition in Heptanchus, that the part-insertion of this muscle on 
the basihyal is a secondary relation, formed in consequence of the diminution of the 
first hypobranchial, and does not prevent this muscle from being regarded as that 
of the first gill-arch. C.br. 2, inserted mainly on the second hypobranchial, but by 
a few fibres also on the second ceratobranchial, runs as a column of muscle to the 
anterior rim of the coracoid. It is in contact with its fellow of the opposite side, 
with which it blends to a certain extent, in the region of its origin ; dorsally the two 
divide, allowing passage for the ventral aorta. C.br. 3 and 4 resemble c.br. 2 in 
origin and insertion, and are found in sequence behind it. They, however, are 
separated throughout their length from their fellows of the opposite side by the 
presence in this region of the pericardium. C.br. 5 presents a greater surface to the 
exterior than any of the foregoing muscles, but is also considerably thinner. It is 
fairly distinctly divided into three portions, all of which, taking origin on the broad 
anterior face of the coracoid, opposite the abductor muscles of the fin, are inserted on 
the inner aspect of the fifth ceratobranchial. 
In Acanthias, the stout columnar muscle which arises on the most anterior portion 
of the coraco-arcual septum, and from it runs forwards and upwards, must be regarded 
as c.br., although its insertion is found to be entirely on the dorsal aspect of the 
basihyal cartilage. As Vetter maintained, the connection of this muscle with the 
hyoid arch is almost certainly a secondary condition, consequent upon the extreme 
reduction of the copula of the first branchial arch; the muscle corresponds in its 
general topography with the muscle which we have described as c.br., in Scy Ilium 
and Heptanchus. Marion also adopts this nomenclature, and therefore, presumably, 
this view of the homology of these muscles. O.br. is separated by a strong aponeurosis 
in the middle line from its fellow of the opposite side. 
The remaining coraco-branchiales (c.br. 2-5) form the lateral wall of the peri- 
cardium. With the exception of the most posterior one (c.br. 5), they are attached 
ventrally not to the coracoid, as in Scyllium, but to a strong fascia which covers the 
dorsal face of the c.a.c. and extends laterally to the superficial branchial muscles. In 
this region they are difficult to distinguish one from another ; Marion regards them 
as a single sheet of muscle. Certainly I have never found them so distinct as is 
indicated by Vetter in his drawing of Acanthias (op. cit., Taf. xv, fig. 8). 
C.br. 2 is inserted into the second hypobranchial ; c.br. 3 and 4 are inserted 
mainly on the third and fourth hypobranchials, but to a slight extent also on the 
corresponding ceratobranchials. C.br. 5 is inserted on the inner aspect of the fifth 
ceratobranchial and (wherein it differs from the corresponding muscle in Scyllium) 
