A Contrilnitioii to the Anatomy of Siren lacertina. (JgJ 



two stages of phylogenetic development, the stage of the sphincter 

 being the earlier. 



If we compare this stage with the next, we find the arytenoid 

 cartilage in B o c c u p y i n g the position of the lateral raphes 

 in A. 



It appeals, in fact, as if the raphe had been replaced 

 by the caitilage, a theory which is certainly reasonable, and 

 which, if we accept it, leads us to the following statements regarding 

 the origin of certain laryngeal parts. 



1) The primordial larynx consisted of a simple muscular tube, 

 divided into four quarters by tendinous raphes, and enclosing the 

 air-passage, the size of the lumen of which it regulated by a sphincter 

 action. The muscular tube itself may be considered as a derivative 

 from the system of pharyngeal muscles. 



2) The arytenoid cartilage arises as a ch oud rif i catio n 

 of the lateral raphes of this primordial muscular tube, 

 the action being changed thereby from a sphincter motion to that of 

 a lever, a relation which persists throughout all the higher Vertebrates 

 including man. 



This chondrification is to be considered as having arisen laterally 

 in the raphe, the process continuing towards the centre in the direction 

 of the arrow. The change of action has this been gradual and prob- 

 ably accidental, becoming first advantageous as a lever action when 

 the cartilage projects from the ring into the interior. 



Of course, as we may scarcely hope to find a more primitive 

 larynx than that of Siren, we must turn from phylogenesis to onto- 

 genesis, and seek in the embryology of this and allied animals, the 

 confirmation or refutation of the preceding, unfortunately AmpMuma 

 is the only one of the lower Urodelans, of which, at the present time, 

 we possess embryonic forms, and that, perhaps, is too specialized an 

 animal to yield conclusive results. 



The cricoid cartilage, from its fibro- cartilaginous structure, as 

 well as from its shape and position, may be apparently considered as 

 a portion of the primordial connective tissue, which anteriorly lies 

 between the muscular ring and the lumen of the tube, and which, 

 below the region of this ring, has secondarily taken upon itself carti- 

 laginous elements, as with the tracheal cartilages. In other words, it 

 is the first of the series of tracheal elements, employed in the service 

 of the larynx, but which even in man bears a close resemblance to 

 the tracheal rings immediately succeeding it. With regard to the 



Zool. Jahrb. IV. Abth. f. Moriih. J.fp 



