The Amphibian larynx. 



301 



muscle (D^. + Fg), the Digastricus pharyngis of Göppert. This 

 muscle, whether representing the ventral segment alone, or with the 

 addition of the dorsal element, lies ventral to the larynx, and oc- 

 casionally (Siren) becomes secondarily attached to some of the 

 respiratory cartilages. Its former name, Hyo-trachealis, expressed 

 thus only an occasional relationship. It is probably absent in the 

 Anura, as the muscle generally referred to it (Verengerer des 

 Aditus laryngis Henle ; Hyo-laryngeus Göppert) proves to 

 be a derivative of the intrinsic ring (F^) [vide infra]. 



1^^ visceral arch (5'h branchial or laryngeal). 



The muscles of this segment are the only ones which properly 

 belong to the larynx. Their derivatives are as follows: 



Dorsal segment: This forms the extrinsic system, with 

 the occasional addition of the muscles of the previous arch when- 

 ever they become attached to the respiratory cartilages. It is vari- 

 ously known as Dorso-trachealis or Dorso-laryngis, in 

 accordance with its variant mode of insertion ; or as the Dilatator 

 aditus laryngis, referring to its action. It always acts as a 

 separator of the respiratory cartilages and thus serves to enlarge 

 the orifice for the passage of air. In many Anura it is separated 

 into two muscles by the growth of the thyroid processes of the hyoid. 



Ventral segment: This is always found in close association 

 with the arytaenoids and forms the intrinsic system. It becomes 

 separated into dorsal and ventral portions by the growth and 

 flattening out of the arytaenoid cartilages (Neciurus) and shapes 

 itself into a ring composed thus of four quarters, two dorsal and 

 two ventral Laryngei (Göppert). This ring becomes variously 

 modified, especially in the Anura. 



The diagram here given expresses the above relations in graphic 

 form. 



Fig. D. 



Diagram of the mus- 

 cles connected with the 

 respiratory apparatus 

 (compare Fig. A). The 

 muscles shaded by dia- 

 gonal lines are e x - 

 trinsic, the muscles 

 dotted, intrinsic. The 

 muscles left white do not 

 participate in respira- 

 tion. 



w. 



^^^^m. 



