THE ALIMENTARY CANAL AND ITS APPENDAGES 173 



greater part, from branchial or visceral structures. 1 It may be 

 considered as certainly proved that the upper part of the thyroid 

 cartilage arises out of the fourth and the lower out of the fifth 

 primitive (i.e. the second and third branchial) visceral arch, and 

 it is probable that the fifth branchial arch gives rise to the 

 arytenoids. 



With regard to the Mammalian epiglottis, it seems now 

 tolerably certain that it does not owe its origin merely to the 

 mucous membrane of the floor of the mouth, but that it repre- 

 sents an originally paired skeletal element which, in the course 

 of phylogeny, has passed from the condition of hyaline- to that 

 of fibro-cartilage. [This view receives support from the investi- 

 gations of Goppert, who has recently given reasons 2 for believing 

 that the cartilages of Wrisberg and the epiglottis, which are 

 frequently in organic continuity among the lower Mammals, are 

 specialised portions of one original structure.] Any attempt, 

 however, to derive the epiglottis from the branchial skeleton 

 seems, in the present state of our knowledge, beset with diffi- 

 culties. 3 



[It is now demonstrated that the upward prolongation of the 

 Mammalian epiglottis involves that organ in a relationship with 

 the velum palatinum (furnishing a raison d'etre for the existence 

 of the latter), for the purpose of restricting the respiratory passage 

 (narial pharynx). Special inquiry has also shown that in both 

 the young and adults of representatives of all orders of Mammals, 

 the epiglottis, when at rest, lies above the velum in an intra- 

 narial position. Man is, however, an exception to this rule, at 

 least in the adult state, and there is reason for believing that 

 the velum and epiglottis have, in him, suffered a loss of connection 

 by the specialisation of the latter more particularly for vocalisa- 

 tion. It is yet uncertain whether the epiglottis of the human 

 embryo does or does not occupy the intra-narial position 4 ]. It 



1 The hyoid and the thyroid skeletal apparatus are still closely connected in Ortiith - 

 orhynchus, and bear distinct traces of their branchial origin, as not only lateral 

 arches, but portions of their median elements or copula can clearly be recognised. 

 In the higher Mammalia the hyoid separates from the thyroid, although the 

 two continue to be related (cf. the cartilago triticea, ante, Fig. 94). In Mammals 

 above the Monotremata the thyroid cartilage appears to consist of a single plate ; 

 but it gives some indications of its primary origin from two consecutive branchial 

 arches which still remain distinct in the Monotremata (Gegenbaur). 



2 [Morph. Jahrb., Bd. xxi. p. 68.] 



3 [Gegenbaur has recently come to the conclusion that the epiglottis is a 

 derivative of the fourth pair of branchial arches, Die Epiglottis, Leipzig, 1892.] 



4 [Cf. Howes, Jmir. Anat. and Phys., vol. xxiii. p. 594.] 



