64 THE SALAMANDER 



fascia lateral to the M. cucullaris and immediately posterior to the 

 muscle just described. It passes ventralwards round the pharynx 

 mesial to the thymus gland, and posterior to the pulmonary arch. 

 It is inserted by means of a strong thread-like tendon — the ligamen- 

 tum dorso-laryngeum (Driiner) — on \}plQ. processus muscularis at the side of 

 the cartilago lateralis of the laryngeal skeleton. The muscle narrows 

 considerably at its insertion and becomes somewhat spindle-shaped. 



The muscle has every appearance of being a serial homologue of 

 the M. cephalo-dorso-subpharyngeus, that is to say, it looks 2iS though 

 it were descended from a levator arcuum branchiarum posterior to 

 the M. lev. arc. branch, iv, and indeed several notable authors have 

 attempted to prove it to be such a muscle. Edgeworth (i 920), how- 

 ever, has shown definitely that this is not the case, and that the re- 

 semblance is apparent rather than real. A more detailed discussion 

 of the various theories concerning the homology of the larynx is 

 given on p. 272. 



Innervation: From the N. intestino-accessorius X by fine twigs 

 which enter the mesial aspect of the muscle, and also by a branch from 

 the R. recurrens intestinalis X which enters the muscle ventrally. 



Function: As its name implies it dilates the larynx and opens the 

 glottis. 



M. constrictor laryngis (Edgeworth) (m.c.l.). 



Constrictor aditus laryngis Henle (1839); Fischer (1843); Druner 



(1901). 

 Ring of Periarytenoideus dorsalis et ventralis . Wilder (1892-6) 



Sphincter laryngis ...... Goppert (1894-8). 



A small but powerful muscle which surrounds the larynx immediately 

 ventral to the glottis. The shape of the whole muscle is much like 

 a napkin ring. The fibres do not pass right round the circle, how- 

 ever, but are interrupted in the middle line, both dorsally and ven- 

 trally, by strong tendinous inscriptions. Most of the muscle fibres 

 arise from, and are inserted into, these inscriptions, but a few of the 

 inner ones have both their origin and insertion confined to the/>^rj 

 laryngea of the cartilago lateralis which the muscle surrounds. The 

 normal direction of the fibres is somewhat oblique so that their ven- 

 tral ends are anterior to their dorsal ends, but not infrequently a 

 small bundle may be found which reverses this order, the ventral 

 ends of its fibres being posterior to their dorsal ends, so that the 

 fibres of this bundle cross those of the main mass. Driiner calls them 

 Fihrae cruciatae. The M. constrictor laryngis is always relatively a 

 more powerful muscle in the adult than in the larva, and is normally 



