The Amphibian larynx. 303 



Dorso-trachealis (D,) and inserted directly in the tracheal cartilages. 

 It is undoubtedly its condition in this form which has suggested its 

 name "Hyo-trachealis". In the Salamandridae, through the failure 

 of the 4th branchial arch, it becomes augmented by Levator a reu s IV, 

 the combined muscle being known as the Digastric us pharyngis. 

 This lies as a broad band on the cardiac side of the larynx 

 (Figs. 27 and 28, Triton) in close proximity to the Dorso-laryn- 

 geus (D7). Regarding the origin of this muscle, the simple Hyo- 

 pharyngeus always arises from the 4th epibranchial (Siren^ Siredon^ 

 Menopoma). In Amphiuma the muscle is double in origin, an anterior 

 slip arising from the epibranchial itself and a somewhat larger pos- 

 terior slip arising from a ligament extending backwards from the 

 dorsal tip of the cartilage, and becoming continuous with the fascia 

 of the trunk muscles. As Digastricus pharyngis, the double 

 . muscle normally arises from the dorsal integument, as in the case of 

 the other Levatores arcuum (Necturus, Proteus) but in Triton 

 (and probably in the other Salamanders) both this muscle and the 

 Dorso-laryngeus form long attenuated bands and insert nearly together 

 into the skull beneath the posterior margin of the Digastricus 

 m a X i 1 1 ae (Fig. 30), the Dorso-laryngeus passing underneath 

 the other, and inserting a little lower down. 



Dorso-trachealis, Dorso-laryngeus (D^). We see this 

 muscle in its most primitive condition in Necturus (Fig. 8) arising 

 from the dorsal fascia in the same series as the other Levatores 

 arcuum and spreading out its insertion over the laryngeal cartilages 

 and the walls of the trachea ; just below the larynx a few of its fibres 

 meet in the median line (Fig. 24). 



The muscle lies pharyngeal to the hyo-pharyngeal muscle (Fg) 

 and overlaps it by its anterior edge. 



Proteus shows two points of difierence. In the first place the 

 Hyo-pharyngeus (= Pharyngo-branchialis 4 = F^) is very much 

 more extensive and underlies the entire larynx and trachea (Fig. 9) 

 and secondly, by the extension of the posterior processes of the 

 Cartilago lateralis down the sides of the trachea, the insertion of the 

 Dorso-laryngo-trachealis (as the muscle may here be designated) be- 

 comes mere definite, and there is no meeting of the fibres in the 

 median line. In Siren and Menopoma this muscle becomes difi"eren- 

 tiated into a Dorso-laryngeus, a narrow band formed by the 

 separation of a few of the anterior fibres, and a Dor so-trachealis 



