THE MUSCLES 63 



transformed larval M. transversus ventralis iv, while the pars dor- 

 salis represents the larval MM.levatores arcuum branchiarum iiiand 

 iv, and the inscription itself takes the place of the atrophied cerato- 

 branchial cartilages iii and iv. The relation of the two parts of the 

 pars dorsalis is also interesting. They are almost always separated 

 by the 'third' aortic arch, or its vestigial remains, so that the portion 

 of the muscle representing the M, lev. arc. branch, iii of the larva 

 passes between the systemic arch and the 'third', while that repre- 

 senting the M. lev. arc. branch, iv passes between the 'third' arch 

 and the pulmonary. The only exception so far recorded is one case 

 reported by Driiner in which the whole muscle passed posterior to 

 the 'third' arch, between it and the pulmonary. 



Innervation: Pars subpharyngea from the R. recurrens n. intesti- 

 nalis X, Pars dorsalis^ anterior portion from the nerve of the fifth 

 visceral (third branchial) arch, and th.^ posterior portion from the R. 

 intestino-accessorius X. These nerves are exceedingly fine and enter 

 the muscle from its mesial aspect. They are best seen from a dorso- 

 lateral view, by separating the muscle from its origin and carefully 

 turning it out laterally, when the nerves may be seen running across 

 the space against the darker blood-vessels beneath. 



Function : One obvious function of the muscle is to constrict the 

 pharynx, and thus it is probably of use in deglutition and respiration ; 

 but, as Driiner rightly points out, the intimate connexion between 

 the insertion of the muscle and the truncus arteriosus may cause it 

 to have some effect on that organ. Again, the distal part of the 

 'third' arch and the ductus Botalli between the pulmonary and sys- 

 temic arches both pass mesial to the pars dorsalis^ so that the contrac- 

 tion of the muscle would tend to compress these vessels against the 

 wall of the throat and may thus have some influence in separating 

 the arterial from the pulmonary blood. It is not possible to estimate 

 its exact function, if any, in this respect without physiological experi- 

 ments on the living animal. 



M. dilatator laryngis (Edgeworth) (m.d.l.). 



Dilatator aditus laryngis . ..... Henle (1839}. 



Dorso-laryngeus et Dorso-trachealis . . . Fischer (1843). 



Dorso-laryngeus et Dorso-trachealis, s. Dorso-branchialis v. 



Wilder (1892-6). 

 Dorso-pharyngeus of Dorso-laryngeus et Dorso-trachealis 



Goppert (1894-8). 

 Dorso-laryngeus .... Driiner (1901); Osawa (1902). 



This muscle is narrow and ribbon-like and arises from the dorsal 



