168 JEREMIAH S. FERGUSON 



Removal of the integument with the adherent constrictor 

 muscles exposes the coraco-mandibularis (fig. 1, B), a slender 

 paired muscle, its two sides intimately fused in the median line, 

 which takes origin by a tendinous fascia from the ventral surface 

 and anterior margin of the coracoid arch. The paired muscle 

 passes forward to its insertion, ending in short, rounded and 

 slightly divergent tendons which are attached to the posterior 

 margin of the inferior mandible. The muscle is inclosed within 

 the folds of a superficial cervical fascia, which forms its aponeu- 

 rosis and extends laterally to the surface of the branchial arches, 

 but on either side of the muscle, the aponeurosis fuses with the deep 

 cervical fascia with which it is in more or less close contact. 



On lifting the coraco-mandibularis with its superficial cervical 

 fascia the coraco-hyoid muscle (fig. 1, C) is exposed; it is similar 

 in shape and appearance to the coraco-mandibular, but is much 

 broader, its lateral margin projecting from beneath the coraco-man- 

 dibularis, and in Mustelus, Squalus and Carcharias extending lat- 

 erally almost to the ventral ends of the branchial clefts, or even 

 overlapping them somewhat. In Raia the gills are more widely 

 separated, leaving a broad portion of the floor of the pharynx 

 exposed at the side of the coraco-hyoideus in the anterior portion 

 of the cervical region. Posteriorly the several divisions of the 

 coraco-branchialis muscle cross this exposed portion of the pharyn- 

 geal floor to be inserted into the branchial arches. 



The ventral surface of the coraco-hyoideus is smooth, its dorsal 

 surface separates into several muscular processes, the musculus 

 coraco-branchialis {M. c. br., fig. 5), to be inserted into the mem- 

 branous floor of the pharynx by a tendinous fascia overspreading 

 and firmly adherent to the fibrous pharyngeal submucosa and 

 the surfaces of the cartilaginous branchial arches. The divergent 

 portion of the coraco-hyoidei, on either side of the median line, 

 are similarly inserted into the movable basi-hyal cartilage (lingual 

 bone), so that the combined coraco-hyoid and coraco-branchial 

 muscles, arising from the anterior border of the coracoid arch, form 

 a very powerful dilator of the mouth and pharynx. 



As the coraco-hyoideus does not extend forward beyond the 

 hyoid arch it exposes the membranous floor of the oro-pharynx 



