74 ME. W. Q. EIDEWOOD ON THE HYOBEAJ^rCHIAL 



together. I fail to see what advantage is to be gained by giving 

 distinct names to the cartilaginous and ossified portions as 

 Grrooberg does (18. p. 636). 



The hinging of the rods is such that they can swing in the 

 horizontal plane, and the free posterior ends are capable of 

 moving through a distance of about 3 "5 millim. each. The 

 hinder parts of the rods can touch one another in the median 

 plane, as may be seen by manipulation, and more conclusively 

 by the flatness of the more projecting parts of their mesial 

 surfaces, where the impact, of which more anon, normally takes 

 place. They are, however, prevented from crossing the middle 

 line by a forwardly directed process of cartilage (PI. 9. fig. 5, cr.) 

 standing up from the inner surface of the posterior part of the 

 floor of the larynx. A similar crest, of much smaller size, hangs 

 down from the roof. The two rods are notched internally, so 

 that they can strike one another without encountering these 

 crests. The rods are actuated by special dilator muscles attached 

 to outstanding processes (PI. 9. fig. 5, d) of the parts situated 

 anteriorly to the centre of oscillation (v). On the contraction 

 of the muscles the anterior parts of the rods are divaricated, and 

 the longer posterior portions are brought into contact. 



Although Mliller (30. p. 222) has compared the rods with the 

 two prongs of a tuning-fork, most authorities liken them to the 

 clapper of a bell. Mayer, for instance, states (25. p. 542) that 

 they are disposed in such a manner, " dass sie an die innere 

 Wandung der Hohle desselben, wie der Schwengel in der Grlocke, 

 anschlagen konnen." Henle erroneously regarded the bones 

 as fixed in position and unable to swing bodily to and fro, and 

 concluded (19. p. 31) that the sound uttered must be due to 

 molecular vibration. Grronberg (18. p. 637) exposed the fallacy 

 of this statement and showed that, although the rods do not 

 swing about fortuitously at every movement of the animal, they 

 are nevertheless capable of motion, and that they are controlled 

 by special muscles attached to them. A study of the muscular 

 mechanism has convinced me that the rods do not beat against 

 the laryngeal walls as a clapper strikes a bell, but that they strike 

 one another in the manner indicated above. It is evident that 

 the larynx is thus curiously modified for the production of 

 sound, and the sound to be expected on a priori reasoning is a 

 series of short, sharp taps caused by the impact of the rods, 

 following one another as quickly as successive contractions of 



