184 
Plethodon. 
The investigation of this genus includes three species (or perhaps 
two and a variety). The largest, P. glutinosus, was used for dis- 
section, of P. cinereus the entire neck region, from the otic region to 
the sternum, was cut into a transverse series, and of P. erythronotus, 
a transverse series was cut which included merely the ventral wall of 
the pharynx and the surrounding parts in the region where the larynx 
might have been expected. ‘The three preparations agreed with each 
other in almost the minutest details and were thus used interchange- 
ably in furnishing the description. A ventral dissection of the region 
involved is given in Fig.1. By the removal of the sternum, shoulder- 
girdle, thoracico-hyoid muscle and heart, the deep muscles of the 
ventral wall of the pharynx are exposed. These are easily recognized 
as the laryngo-tracheal muscles found in normal forms. They con- 
sist of two pairs of narrow bands which come around the body from 
the dorsal region and meet in or near the mid-ventral line in close 
relation to the upper portion of the pericardium at the point where 
it is reflected about the bulbus arteriosus. The more anterior of 
these is the larger, and arises from the otic region of the skull 
(Fig. 2 dig. ph.). 
Upon the ventral side, as it passes around the edge of the 
pharynx, a tendinous raphé passes completely through its fibres, divid- 
ing it into dorsal and ventral portions. The raphé is the rudiment 
of the 4th epibranchial, and the muscle thus represents both dorsal 
and ventral elements associated with the 4th branchial arch!). It is 
thus dorso-branchialis, + pharyngo-branchialis, and 
may be designated by GÖPPERT’s ?) name, digastricus pharyngis. 
The muscle immediately posterior to this arises from the dorsal 
integument and, running around the body exactly at right angles to 
its longitudinal axis, is cut by a transverse series throughout its 
entire extent (Fig. 4, dors. laryng.). In Salamandrids possessing a 
larynx, a muscle similarly placed is inserted upon the arytaenoids and 
acts as a dilator of the aperture. It is opposed by the dorsal and 
ventral ring muscles, the laryngei. The two taken together 
(dorso-laryngeus — laryngei) probably correspond to the 
dorsal and ventral segments of the 5th branchial arch (= arytaenoids). 
With the reduction of this arch come two possibilities: first, that the 
cartilage might simply drop out as in the case of the 4th epibranchial 
1) See my paper “The Amphibian larynx”. Zool. Jahrb., Abt. f. 
Morph., Bd. IX, Heft 2. 
2) Görrert, Die Kehlkopfmuskulatur der Amphibien, Morph. Jahrb 
VY. 22, Heft 1, 1894. 
