VISCERAL ARCHES OF THE GNATHOSTOME FISHES. 353 
muscles in embryos, and that the coracobranchiales of Vetter’s 
descriptions are not each derived from the ventral end of the 
corresponding branchial myotome, as they are said to be by 
both those authors. 
The coracobranchiales of these fishes must then either be 
developed from trunk myotomes, as the eoracohyoideus and 
coracomandibularis are said to be ; be developed, as in 
Ceratodus (Greil), from the ventral end of the axial mesoderm 
of the ultimate branchial arch, as will be later explained ; or, 
possibly, be developed from some part of the coelomic wall. 
Their innervation, as at present given, is decidedly against 
the supposition that they are developed from the myotome of 
the ultimate branchial arch, and in favour of their being- 
developed from trunk myotonies, as the other hypobranchial 
muscles are said to be. The conditions in Chlamydoselachus, 
if this fish is as primitive a one as it is generally considered 
to be, would favour their being developed from the coelomic 
wall, and this derivation has been ascribed to them, in other 
Selachii, by van Wijhe. 
Van Wijhe says (1882 b, p. 16): “ Der Muse, coraco- 
branchialis + coraco-mandibularis hat eine ganz andere 
Entstehungsweise als der coraco-hyoideus. Er entwickelt 
sich namlich aus der unpaaren vorderen Verlangerung des 
Pericardiums, dessen Hohle, wie wir gesehen haben, im 
Stadium J mit den Holden der Visceralbogen communicirt. 
Nach dem Stadium K fangt diese vordere Verlangerung zu 
obliteriren an ; die Zellen ihrer Wande werden Muskelfasern, 
und im Anfang des 0 ist die ganze Hohle geschwunden ; 
ihre muskelosen Wande sind zusammengekommen, undbilden 
die Anlage des Muse, coraco-mandibularis -f coraco-bran- 
chialis. In spaten Stadien ist derselbe immer leicht von dem 
Muse, coraco-hyoideus zu unterscheiden. Die Nebenzweige, 
welche ersterer zu den Visceralbogen abgeibt, sind aus den 
Unterenden der Wande der Visceralbogenhohlen entstanden.” 
The iC Nebenzweige ” above referred to by van Wijhe are 
quite certainly simply the deeper, proximal fibres of the 
ventral portions of the constrictores superficiales, which 
