62 ME. W. G. EIDEWOOD ON THE HTOBEANCHIAI, 



which, behind the glottis, meet one another in the median plane 

 by perfectly flat and smooth articular surfaces *. These masses 

 of cartilage lie immediately in front of the thickened anterior edge 

 of the roofing cartilage of the larynx and usually contain a small 

 centre of ossification each. These ossifications, like those of the 

 posterior epiphyses of the thyrohyals and the anterior part of 

 the floor of the laryngeal complex, only appear with advancing age. 

 A female may be fully grown and sexually mature without 

 exhibiting a trace of ossification in these regions. The lateral 

 motion of the arytenoids is limited by a pair of concavo-convex 

 upgrowths of the side-walls of the larynx (PI. 8. fig. 3, hi.), called 

 by Henle (p. 17) the " Scheublappenartige Eortsatze" or blinker- 

 shaped processes. There are no vocal cords, and their absence 

 may account for the exceptional shape and mutual relations of 

 the arytenoids. The failure of the arytenoids to touch one 

 another in front of the glottis is also a matter of no little 

 importance. 



The relations that obtain between the cricoid cartilage of 

 Xenojpus and that of other Anura can best be made out by the 

 study of a median section of the laryngeal skeleton. By this 

 means it is seen that the roofing part of the larynx of Xenopus 

 (PI. 8. fig. 2, c) is nothing more than the median dorsal rod, 

 greatly expanded, of Sana esciilenta (PI. 9. fig. 7, c), while the 

 floor (PI. 8. fig. 2, c'c") is made up of the coalesced enlarged 

 transverse bars (PI. 9. fig. 7, c & c"). Even the blinker- 

 shaped processes of Xenopus (PL 8. fig. 3, II.) can be recognized 

 in the frog's larynx in the swellings (PI. 9. fig. 7, hi.) at the 

 sides of the anterior ventral bar of the cricoid. The mem- 

 branous area (PI. 8. fig. 2, /) in the side-wall of the larynx of 

 Xenopus is a great guide in the determination of the parts, since 

 it fixes the position of the space (PI. 9. fig. 7,f) at the sides of 

 the ring of cartilage on the ventral surface of the frog's larynx. 

 Owing to the great expanse of cricoid cartilage in Xenopus, the 

 connexion with the posterior epiphysis of the thyrohyal, situated 

 in the frog close behind the arytenoid (PI. 9. fig. 7, V), is thrown 



* Seeing that in the larval larynx (Pi. 11. fig. 10) the arytenoids are in 

 contact with the anterior edge of the dorsal part of the cricoid, and are even 

 overlapped by it, it becomes doubtful vrhether, after all, the massive part of 

 the arytenoid of the adult is a process of the true arytenoid — it may be simply 

 an enlargement of the posterior end. In the male of Pipa it is tolerably certain 

 that the bulk of what is known as the arytenoid is really a process of the true 

 arytenoid ; but the relations are simpler in Xenopus. 



