80 ME. W. G. KIDEWOOD ON THE HXOBEANCHrAL 



division of the compressor (his " sphincter posterior ") arise from 

 the cricoid cartilage, a fact which Henle had previously recorded 

 (19. p. 24) but in a somewhat unsatisfactory manner. 



The middle of the compressor muscle is tendinous and closely 

 bound to the external face of the arytenoid over a narrow area 

 extending backwards and outwards from the middle of the length 

 of the glottis. "While the dilator anterior muscle is to all intents 

 and purposes connected with the arytenoid cartilage, it would be 

 more correct to say that it is inserted into the tendinous middle- 

 tract of the compressor, which in its turn is bound to the ary- 

 tenoid. For, when the compressor is removed bodily from the- 

 skeletal parts, the dilator anterior muscle is found to be still very 

 tightly bound to it, showing that the fibres do not simply decus- 

 sate. The same treatment also shows that the two bellies, 

 anterior and posterior, of the compressor cannot well be regarded 

 as distinct muscles. Under any circumstances, they cannot 

 be individually homologous with the two muscles running along- 

 side the glottis in the frog, although the digastric compressor of 

 Xenopus is probably equivalent to the two muscles of the frog 

 taken collectively. 



The muscles in the immediate vicinity of the glottis in Anura^ 

 are subject to extreme variation, even in genera which are ad- 

 mitted to be closely allied. Henle made a comparative study of 

 these muscles, and Wilder has latterly reconsidered the subject. 

 "Wilder acknowledges that the study is a most confusing one ;. 

 hut he has arrived at the conclusion (42. p. 308 et seq.) that the 

 primitive periglottidean muscle in Anura is a sphincter surround- 

 ing the arytenoid cartilages and unconnected with the thyrohyals.- 

 The muscle may remain as such unchanged {Bomhinator^), or 

 part of it may become differentiated into a compressor and a 

 constrictor, while part remaius as a sphincter {liana) ; or the 

 entire muscle may differentiate into compressor and con- 

 strictor {Bufo). The compressor and constrictor both acquire 

 a secondary connexion with the thyrohyal. Of Xenopus he says 

 (42. p. 313), "The sphincter in Dactylethra appears very simple, 

 divided into four quarters by median and lateral raphes," and he- 

 notices that the " lateral raphes appear to be connected with the 



* Henle is in error in describing (19- p. 24) a connexion between the com- 

 pressor muscle and the hyobranchial skeleton in Bombiriator and Discoglossus. 

 I have examined the muscle in these genera and find it to be an intrinsic 

 laryngeal in both. 



