SKELETON AT^D LARYNX OP XEISTOPIIS AND PIPA. 81 



metliod of insertion of the Dilatator." He fails, however, to note 

 that the anterior ends of the sphincter muscles are attached, not 

 to the arytenoid cartilages or one to another, but to the portion 

 of the hyobranehial cartilage between the anterior ends of the 

 thyrohyal bones. This fact leads me to think that the periglotti- 

 dean muscles of Xenopiis are not so simple as he makes out, and 

 that they do not represent an undifferentiated sphincter such as 

 occurs in Bombinator. Wilder says (42. p. 307) that in a late 

 larval stage of the tadpole of Sana the as yet undivided sphincter 

 attaches itself to the inner edges of the two thyroid processes. 

 This occurs before the constrictor and compressor have been 

 differentiated, and it is just this stage of development which, I 

 take it, persists in Xenopus. The periglottidean muscle of 

 Xenopus may therefore be regarded as including an undiffer- 

 entiated constrictor ; and the absence of any muscle which can 

 with certainty be regarded as the constrictor laryngis lends 

 support to the view. 



Syoglossus. — Turning now to the ventral aspect of the larynx, 

 three important muscles are to be noted : — the hyoglossus, the 

 geniohyoideus internus, and the petrohyoideus. The hyoglossus: 

 (Hyoglossus, Henle, 19. p. 26) consists of three separate bellies, 

 the external of which (hyoglossus externus, PI. 10. fig. 1, h.e.) 

 arises from the ventral surface of the thyrohyal at about the 

 middle of its length ; while the middle division, — which Henle 

 (19. p. 26) erroneously declares to be absent in Xenopus, although 

 he mentions it as occurring in Pipa, — takes its origin from the 

 floor of the larynx at about one-third of the length from the 

 anterior end (fig. 1, h.i.). Mayer (26. p. 30) calls the hyoglossa 

 muscle of Anura the ceratoglossus, and states that it appears to 

 be wanting in Xenopus, — clearly an error of observation. He 

 considers it equivalent to the muscle which he had previously 

 called the laryngoglossus in Pipa (25. p. 537, and fig. 2, e). 



The middle division of the muscle, the hyoglossus internus, is 

 really double, and the two halves are at their origin perfectly 

 distinct. But anteriorly they unite in the median plane, and at 

 the front of the larynx they are inseparable. The external 

 divisions arising from the thyrohyals, although closely applied to 

 the internal division, do not fuse with it. The three muscle- 

 trunks, after running forward ventral to the laryngeal cartilage 

 and dorsal to the m. geniohyoideus internus (PI. 10. fig, 1, g.i.), 

 are still readily separable as they pass upward, immediately in 



LINN, JOUEN. — ZOOLOGY, VOL. iSTI. 6 



