OP ARTS AND SCIENCES. 115 



While Giinther ('42, pp. 32, 56) agrees with Reichert as to the 

 division of the external portion of the cleft into two parts, he disagrees 

 entirely as to the fate of these parts. The edges of the first cleft fuse 

 at first in the middle, so that instead of one there are two openings, 

 the lower (ventral) of which suffers no metamorphosis and soon dis- 

 appears entirely. The upper orifice is converted, the outer parts into 

 the external parts of the ear, the inner into the tympanum and Eusta- 

 chian tube. 



In his text-book BischofF ('42, p. 410) follows in the main the con- 

 clusions reached by Reichert, but, contrary to that author as well as to 

 Rathke, he places the partition which separates the inner from the outer 

 part of the cleft midway between the two ends, " in the middle of the 

 thickness of the two arches." 



According to Kolliker ('61, pp. 321, 322), the first cleft is closed in 

 the human embryo in the fifth week ; not, however, in its totality, like 

 the other clefts, but so that on both sides of the place of union — 

 which lies near the external orifice — the outer and inner ends remain 

 open, and are respectively nothing else than the beginning of the ex- 

 ternal meatus and of the Eustachian tube and tympanum. The region 

 of the union represents the primitive tympanic membrane. Subse- 

 quently the inner part of the cleft increases in length, and gradually 

 becomes wider at its hinder or outer end. 



In his lectures Rathke ('61, p. 117) taught that the first cleft in 

 frogs and many toads, as well as in turtles and saurians, is only closed 

 near its outer end, and from the substance effecting the closure is 

 formed the tympanic membrane ; in the case of birds and mammals, 

 however, that it is closed at about the middle of its depth, and that the 

 outer half of the cleft becomes the external meatus, while the inner 

 becomes the Eustachian tube and tympanum. 



In 1876 Hunt presented to the International Otological Congress a 

 paper embracing " a new account of the development of the meatus 

 externus, drum, and Eustachian tube." The whole paper was re- 

 printed in the following year (Hunt, '77), and the substance of so much 

 of it as relates to the meatus externus, etc. was also embodied in a 

 paper published by the author in the same year in the American 

 Journal of the Medical Sciences (Hunt, '77^). 



In these papers Hunt ('77% p. 1) says: "At the same time Von 

 Baer stated an opinion as to the development of the meatus and Eu- 

 stachian tube that was opposed by Iluschke ; here also the latter was 

 declared victor, but I believe incorrectly." Hunt maintains tliat the 

 external meatus is derived, at least in part, from a furrow formed at 



