577 
continuing, with change of relation, throughout the group. The two 
elements are as follows. 
1. M. hyo-trachealis. 
This is the more inconstant of the two. Well developed in 
Siren and Amphiuma, it occupies a position as a deep trans- 
verse layer, stretching from the hyoid apparatus (4th Epibranchial in 
Siren, 3rd and 4th in Amphiuma) across to the cartilaginous 
elements of the trachea. In Siren it is supplied by a branch of its 
own, which arises from the Vagus in close relationship to the recur- 
rent branch, but in all others it receives innervation directly from the 
latter. 
In Menopoma it lies superficially as a Hyo-laryngeus and 
appears as a narrow band which joins its opposite in the median line, 
the junction taking place upon the larynx, but showing no immediate 
connection with it. In Siredon the Hyo-trachealis appears as an 
Interhyoideus, meeting its opposite anterior to the entire respi- 
ratory tract. Here we take leave of it, a muscle which, apparently 
having wandered forward from a tracheal attachment to a laryngeal, 
and from this to an antelaryngeal, finally disappears from the field 
altogether. 
2. M. dorso-trachealis. 
3. M. dorso-laryngeus. 
Under these names a group has been described which exists in 
its typical form in Amphiuma, Menopoma and Siren, where 
the first muscle, a broad radiate sheet, arising from the dorsal fascia, 
attaches along the side of the trachea, while a band upon its anterior 
margin becomes differentiated from it and is inserted into a lateral 
process upon the Arytaenoid (Dorso-laryngeus). In Siredon, a 
complete separation has been effected between these two bands, and 
the dorso-laryngeus, lying at its origin posterior to the other, crosses 
beneath it to gain its customary position. In Triton these two 
bands become attached, the one to the lateral processes of the Arytae- 
noid, the other, farther forward, near the anterior ends of the carti- 
lages just mentioned. 
In Salamandra, the anterior band has no connection with the 
larynx, but meets its fellow in the middle line anterior to the air- 
passages, while the posterior band is related as in Triton. We see 
thus in this series a gradual forward movement and subsequent dis- 
appearance of the dorso-trachealis, similar to the fate of the 
hyo-trachealis given above. Here the dorso-laryngeus remains con- 
stant throughout the group, the change of relative position being due 
38 * 
