. The Bashford Dean memorial volume :. Fishes; Sharks; Fishes, Fossil. The Ayiatomy of Chlamydoselachus 389 muscles of the body and tail—as in Scyllium (Van Wijhe, 1883, p. 36 and Fig. 25, Taf. Ill); in Lacerta (Corning, 1895); in Fctromyzon and Squalus (Neal, 1897); and in Lepido- siren and Frotopterus (Agar, 1907). In Heptanchus (Davidson, 1918) the following muscles (Text-figure 63) are recognized as members of the hypobranchial group: the paired coracoarcu- ales communes (car.), the unpaired coracomandib- ularis (), the paired coracohyoidei (), and seven pairs of coracobranchiale
. The Bashford Dean memorial volume :. Fishes; Sharks; Fishes, Fossil. The Ayiatomy of Chlamydoselachus 389 muscles of the body and tail—as in Scyllium (Van Wijhe, 1883, p. 36 and Fig. 25, Taf. Ill); in Lacerta (Corning, 1895); in Fctromyzon and Squalus (Neal, 1897); and in Lepido- siren and Frotopterus (Agar, 1907). In Heptanchus (Davidson, 1918) the following muscles (Text-figure 63) are recognized as members of the hypobranchial group: the paired coracoarcu- ales communes (car.), the unpaired coracomandib- ularis (), the paired coracohyoidei (), and seven pairs of coracobranchiales (). In elas' mobranchs generally, according to Daniel (1934, p. 108), all of these muscles excepting the coraco' branchiales arise from the first five trunk myotomes. Edgev^orth (1903) states that in Scyllium the coraco- branchiales develop from head myotomes. In the adult Heptanchus, the metameric nature of the cora' coarcuales is attested by the presence of a series of four transverse or sHghtly oblique myosepta (Text- figure 63). In the coracoarcuales of Scymnus, there are five such myosepta (Fiirbringer, 1897, Fig. 3, Taf. VI). In Heptanchus, Vetter (1874, Fig. 9, pi. XV) shows a myoseptum in the coracohyoideus muscle also. The hypobranchial group of muscles is often called the hypoglossal musculature because the mus- cles of this group are supplied, somewhat indirectly, by a nerve which, variously called the spino-occipi- tal, occipital or hypoglossal nerve in fishes and am- phibians, in the higher vertebrates is known as the hypoglossal (hypoglossus) or twelfth cranial nerve. This nerve is a composite structure, made up from a series of roots representing, perhaps, several neuromeres. AlHs (1917 and 1923) does not distinguish the hypobranchial muscles of Chlamydoselachus as a separate group. However, he describes the distribution of the branches of "a large nerve which was not traced upward to its origin, but which is either of spinal, or spinal and occip
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