310 ia. H. WILDER, 



other forms, and is the only one inserted into the arytainoid region. 

 It arises from the inner side of the osseous portion of the thyroid 

 process and converges to its insertion by a tendon in the region of 

 the rudimentary arytaenoids. It is probable that Bactylethra re- 

 sembles Pipa in its laryngeal muscles, the various elements just 

 described corresponding to the complicated Dilatator carefully de- 

 scribed by Grönberg (No. 8). Lack of material must however leave 

 this point at present undecided, and it is probable that no definite 

 homologies can be established in this particular between the Aglossa 

 and the other Anura, until the subject receives careful consideration 

 from the side of the development. 



The remaining muscles of the Anuran larynx can undoubtedly be 

 referred to the differentiation of the Sphincter laryngis, yet the 

 course of this dififerentiation is not to be obtained absolutely from the 

 consideration of adult forms and we cannot be certain of the homo- 

 logies in all cases until the embryology of the larynx is studied in 

 each Anuran family. The complex development in Rana which has 

 resulted in the formation of seven pairs of muscles, has been already 

 subject to consideration. 



Of these seven pairs it will be remembered that four owe their 

 origin to the development of the anterior pharyngeal processes of the 

 annulus, viz : the dorsal and ventral portions of the sphincter, and the 

 the two accessory portions of the Dilatator. If .we imagine a form 

 that does not develop these processes, we will see that the entire 

 ventral half of the original Sphincter will be included in the Con- 

 strictor, and the entire dorsal half will become the Compressor. The 

 little accessory bundles of the Dilatator will not develop. This con- 

 dition is exactly realized in Bufo, the cause of which is evident 

 (Fig. 42). 



Alytes obstetricans admits of only an unsatisfactory explanation. 

 The Dilatator (Fig. 36) is normal. The muscle below this, upon the 

 pharyngeal side, meeting in the median line suggests the Constrictor 

 of Bufo and Rana, but on following it around, we find that it is not 

 attached to the thyroid process, but continues around the larynx upon 

 the cardiac side, nearly completing the circle. It may thus represent 

 more than the pharyngeal half of the Sphincter, or perhaps the entire 

 ring. This leaves unexplained a pair of muscles upon the cardiac 

 side. For this my only explanation at present is that it seems to 

 represent the Constrictor, although its extreme cardiac position is 

 unusual. 



