SKELETON AND LAETNX OF XEISTOPUS AND PIPA. 59 



fused with the anterior edge of the cricoid cartilage of the floor 

 or ventral wall of the larynx, in the position marked ce in fig. 1. 

 The reasons for fixing this as the region of coalescence are based 

 upon a comparison of the cricoid skeleton with that of the frog 

 (see p. 62) and on a study of the development of the parts (see 

 p. 100). The distance t/se, therefore, in fig. 1 represents the very 

 greatly diminished antero-posterior diameter of the large basal 

 plate of the frog's hyobranchial skeleton. Henle has already 

 pointed out in the middle of the basal cartilage of Xenopus an 

 incipient ossification, which he compares (19. p. 17 footnote) with 

 that larger V"shaped ossification which occurs in the middle of 

 the body of the hyoid of Alytes. The ossification occurs only 

 late in life, so that it is quite possible for the larynx of a sexually 

 mature X.enopus to show no trace of it. 



Externally to the region of coalescence between the laryngeal 

 cartilage and the basal plate, and separated from it by two small 

 membranous areas, are the anterior ends of two rods of bone 

 which project backwards and, diverging slightly, run along the 

 right and left sides of the larynx proper (Pi. 8. fig. 1, f). These 

 rods are circular in section, are thicker behind than in front, and 

 are narrowest at a short distance from the anterior end. The 

 posterior epiphyses are cartilaginous and exhibit, in fully grown 

 specimens, an incipient endochondral ossification (PI. 8. fig. 3, ep.). 

 The epiphysis is fused mesially with the hind end of the lateral 

 walls of the cricoid cartilage. The rods are the only fully ossified 

 parts of the whole hyobranchial and laryngeal skeleton ; and in 

 this respect, as also in form, they resemble the columellae or 

 thyrohyals of the tongued Anura *, with which they have been 

 considered homologous by all writers who have given attention 

 to the subject, from Henle onwards. The attachment of the rods 

 to the hind part of the basal plate, their lateral position with 

 regard to the larynx proper, their divergence even, all point to 

 the same conclusion ; and, since I hope to prove in the following 

 pages that all the salient features of the cricoid and arytenoid 

 cartilages of the larynx of the frog or other auuran can be dis- 

 tinctly recognized in the cartilaginous apparatus that lies between 

 the two bony rods in the female Xenopus, there would appear 

 to be here sufficient evidence, without having recourse to that 

 afforded in addition by a study of the relations of the muscles, 

 * Ossifications in the body or basal plate occur in Bomhinator, Alytes, and 

 other forms ; but even in these the cohimellse are the most completely ossified. 



