306 
EDWARD PHELPS ALLIS. 
deeper and superficial portions, which Dolirn calls respectively 
the proximal and distal portions of the myotome, proximal 
meaning nearer the pharyngeal cavity and distal farther from 
that cavity. The separation of the myotome into these two 
parts did not apparently extend, in the embryos examined by 
Dohrn, the full dorso-ventral length of the myotome, for 
Dohrn definitely says that the dorsal ends of the two portions 
of the myotome remain attached by a thin intervening 
portion. The complete separation said to be found in the 
adult must accordingly take place in later embryonic, or 
possibly in postembryonic stages. 
The cartilaginous bar of the arch, when it first begins to 
develop, is said by Dohrn to lie against the posterior surface 
of the proximal portion of the myotome at about the middle 
of its length, and the bar, as it develops, is more curved than 
the myotome. The proximal portion of the myotome thus 
stretches across the morphologically anterior but actually 
lateral surface of the curved bar, projecting, in the middle 
of its length, mesial to the bar, and there acquiring a position 
internal instead of external to it. This middle section of the 
proximal portion of the myotome is later cut out of the 
myotome along the line where the myotome crosses the bar, 
and from the portion so cut out the musculus adductor arcus 
visceralis is said to be developed. The remainder of the 
myotome is said to remain external to the branchial bar, and 
from those parts of its proximal portion that lie dorsal and 
ventral to the piece cut out to form the adductor, and hence 
also dorsal and ventral to the curved branchial bar, the 
musculi interarcualis and coracobrancliialis are said (loc. 
cit., p. 115) to be respectively developed ; these two muscles 
and the adductor thus being primarily continuous and forming 
the entire length of the proximal portion of the myotome 
(loc. cit., p. 117). 
The dorsal and ventral ends of the myotome, including both 
its proximal and its distal portions, are each said to bend 
posteriorly across the dorsal or ventral edge, respectively, of 
the next posterior gill-pouch (Kieinenspalte), and from that 
