THE SHOULDER GIRDLE AND PECTORAL FIN OF FTSHES. 
551 
The nervous supply is derived from the anterior branch of the united ventral 
roots of spinal nerves I and II. 
(iii) Coraco-hyoideus (c.hy.). Coraco-hyoideus, Vetter, Jaquet. 
There is a marked dissimilarity in the two types under consideration in respect 
of this muscle. 
In Chimsera it arises from the anterior face of the V-shaped septum described 
above, its outermost fibres being attached further back and more superficially than 
the median ones, since the latter are displaced by the origin of the deepest portion 
of the coraco-mandibularis. The median fibres meet their fellows of the opposite 
side, but do not fuse with them ; from this median line of contact the muscle masses 
of either side slope downwards and outwards, thus forming the furrow in which runs 
the keel of the c.m. The insertions of the c.hy. of both sides are contiguous, and 
occur upon the postero-dorsal aspect of the basihyal cartilage. 
There is another muscle mass, which Vetter regarded as the posterior portion of 
the c.hy., and which must probably be regarded in part, at least, in that light. Arising 
from the anterior border of the girdle, from just above the origin of the c.m. to the 
level of the glenoid border (where it is covered by the c.br.), the fibres of this muscle 
run downwards and slightly outwards to their insertion on the posterior face of the 
V-shaped septum. Since not only the fibres of the c.hy. are attached to the anterior 
face of this septum, but also those of the c.m. 2, the muscle may be compared to the 
coraco-arcualis communis of Selachians. Pending further evidence, I do not propose 
to alter Vetter’s description of the coraco-hyoideus of Chimsera. 
In Callorhynchus the c.hy. is a relatively slender paired muscle which, arising 
from the dorsal aspect of the c.m., runs forward to its insertion on the basihyal 
cartilage. There is no manifestation of a posterior portion of the muscle connecting 
it with the coracoid, such as has been described for Chimsera. It is not implied that 
no fibres of the' c.hy. reach the coracoid, but that any such are so completely blended 
with the huge c.m. that they cannot be distinguished from it. In fact, the neck 
muscles of Callorhynchus have attained a state of fusion which would render com- 
parison with the Selachian type obscure, were it not for the intermediate condition 
which has been observed in Chimsera. 
(iv) Coraco-mandibularis (c.m.). Coraco-mandibularis, Vetter, Jaquet. 
The coraco-mandibulares of the Holocephali expand anteriorly, and their tendinous 
insertions cover nearly the entire ventral aspect of the mandible. There is a fairly 
distinct division of the insertion into an outer, superficial portion (c.m. 1 of Vetter) 
and a median, deeper portion (c.m. 2 of Vetter). The latter is an azygous muscle, 
composed of the united median fibres of the c.m. of either side. The central portion 
is not severed completely from the lateral portions, for the deeper fibres of both 
portions are in contact ; the fascial fold which serves to separate the muscles super- 
ficially is sufficiently diagnostic to be of descriptive value. 
