544 
CAPTATN E. W. SHANN ON 
Galeus, where it extends almost to the coracoid bar, and least in Acanthias, 
where it extends less than three-fifths of the distance between the basihyal and 
the coracoid. 
In Rhina this muscle is exceedingly short, but of great strength, and is inserted 
on the ventral aspect of the ceratohyal as well as upon the basihyal. On the latter 
it is inserted through the medium of a strong tendon ; moreover, the insertion is 
diagnostic in showing an unpaired median portion, formed by the union in that area 
with its fellow of the opposite side. 
In Raia this muscle is very much reduced, probably in correlation with the 
development of a muscle, the coraco-hyomandibularis, to be described later. I have 
been able to verify Marion’s observation that, arising from the fascia covering the 
c.h.m., it is inserted upon the minute hypohyal cartilage. 
(v) Coraco-hyomandibularis (c.h.m.). Coraco-hyomandibularis, Marion. 
Of the types examined, this muscle occurs only in Raia. In that form it is 
present as a large strip of muscle — the strongest, in fact, of all the ventral muscles — 
which, arising from the fascia limiting the coraco-arcuales communes as far forward 
as the fork of the ventral aorta, runs outwards and forwards (passing dorsal to 
the first hypobranchial) to its insertion on the antero-ventral aspect of the hyo- 
mandibular cartilage. 
(vi) Coraco-mandibularis ' (c.m). Depressor mandibuli, Owen ; Coraco- 
mandibularis, Vetter, Wiedersheim, Tiesing, Marion, etc. 
This muscle arises from the coracoid bar in the ventral middle line, or, more 
frequently, from the coraco-arcual septum ; it is the most superficial of the series of 
muscles under consideration, and, passing forwards in a straight line, 'becomes inserted 
on the posterior border of the mandible. - The muscle may be either azygous or 
divisible into two portions ; it is not divided by myocommata. 
In Scyllium and G-aleus the c.m. is tolerably distinct from its fellow of the 
opposite side, owing to the presence of a longitudinal septum in the ventral middle 
line ; this is particularly noticeable in the region of insertion on the mandible. 
In Acanthias the c.m. is an azygos muscle. The length of this muscle varies 
inversely with that of the coraco-arcualis communis ; thus, in Galeus the muscle 
is of great relative length, almost touching the coracoid bar, while in Acanthias 
it is relatively short. 
In Rhina the c.m. is entirely wanting. 
In Raia the c.m. is a thin strip of muscle, separated by a fascia from its fellow of 
the opposite side, extending from the mandible direct to the anterior border of the 
coracoid itself. Right up to its origin on the coracoid it is distinct from the other 
muscles of the coraco-arcual system. 
