78 ME. "W. a. EIDEWOOD ON THE HTOBEANCHIAL 



(see 13. p. 318). Wilder figures in Bana clamitans (42. Taf. 20. 

 fig, 32, t') an accessory slip of the dilator arising from the 

 ]aryngeal cartilage instead of the thyrohyal, an exact counterpart 

 of this slip in Xenopus. 



Dilator laryngis anterior (PI. 10. fig. 2, d.a.). — This muscle, 

 the "oberer Erweiterer" of Henle (19. p. 27, and Taf. 2. fig. 5, m'), 

 arises from the external surface of the anterior part of the thyro- 

 hyal and extends over rather less than one half its length. It 

 is inserted into the dorso-external surface of the arytenoid car- 

 tilage, in a line passing obliquely across the compressor muscle 

 (c), which is peculiarly modified in consequence. No sharp line 

 of separation can be distinguished between this muscle and the 

 dilator just described, with which its fibres form a continuous 

 series. So far as can be made out, the junction is oblique, the 

 hinder part of the dilator anterior overlapping the front part of 

 the dilator. Both muscles run from the thyrohyal to the aryte- 

 noid, and the insertion of the dilator anterior is in a continuous 

 line with that of the larger muscle (see the dotted line on the 

 left side of fig. 2, PL 10). The fibres of the two muscles com- 

 mingle externally as they arise from the thyrohyal, so that were 

 it not for the greater distinctness and more marked individuality 

 of the muscle under consideration in the male Xenopus and in 

 the female Pipa, there would not be sufiicient evidence to justify 

 the conception of it as a separate muscle worthy of a distinctive 

 name. It is a muscle which has arisen in all probability by the 

 separation of the anterior part of the normal dilator laryngis, 

 and may therefore be designated the " dilator laryngis anterior." 



The only other determination which is at all plausible is that 

 it represents the " constrictor " muscle * of other Anura, which 

 has shifted back along the side of the glottis instead of uniting 

 with its fellow of the opposite side in front. The constrictor 

 normally arises from the thyrohyal and runs on the anterior side 



* Hyo-pre-glottique, Duges, 10. P- 126, and PI. vii. (bis), fig. 47, no. 25. 

 Verengerer des Aditus laryngis, Henle, 19. p- 24 and Constrictor, 19. 



Taf. i. fig. 42, n. 

 Constrictor aditus laryngis, Ecker, 12- p. 315. 

 Peri-arytenoideus ventralis. Wilder, 41- 

 Hyo-laryngeus, Goppert, 16- P- 63. 

 Constrictor laryngis, Wilder, 42- Taf. 20. fig. 31, cs. 

 Saint-Ange (36) does not distinguish between the constrictor and the 

 dilator. He calls them both " dilatateurs " (p. 421), and marks them d and 

 d' in fig. 3', PI. 26. 



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