DEVELOPMENT OF THE PHARYNX AND NECK. 33 



(1) The external auditory meatus from the external cleft 

 depression ; 



(2) The Eustachian tube from the internal cleft recess. These 

 two parts of the first cleft are separated by the cleft membrane 

 which becomes the membrana tympani. 



If traces of the other clefts remain as fistulae or cysts they 

 will occur in the positions shown in figure 25. Part of the 

 second cleft is marked in the goat by an opening and auricular 

 appendage. 



Within the pharynx traces of inner cleft recesses are to be 

 seen besides the Eustachian opening (Eig. 33, p. 43). The tonsil 

 is developed in the second cleft ; the palatoglossus in the 

 anterior pillar of the fauces represents the second arch. The 

 lateral recess of the pharynx (fossa of Eosenmiiller), behind the 

 Eustachian tube, represents the upper end of the second cleft. 

 The pyriform fossa, at each side of the laryngeal aperture, re- 

 presents the fourth cleft (See Fig. 33). 



The Cartilages of the Arches. — The history of the skeletal 

 basis of the first arch (Meckel's cartilage) has been already traced 

 (p. 14 and Figs. IOC and 12). 



The cartilage of the 2nd or hyoid arch forms (Fig. 26) : 



(1) The tympano-hyal, which is imbedded in the petro-mastoid. 



(2) The stylo-hyal (Fig. 26), which ossifies in the early years 

 of life and becomes joined to the tympano-hyal to form the 

 styloid process. 



(3) The segment below, the epi-hyal, which becomes ligamen- 

 tous, and forms the stylo-hyoid ligament, but it also may 

 become ossified. 



(4) The lowest segment, the cerato-hyal, forming the small horn 

 of the hyoid. 



The epi-hyal lies behind and outside the tonsil, and when 

 ossified has been excised under the belief that it was a foreign 

 body. The body of the hyoid (basi-hyal) probably represents the 

 fused ventral parts (copulae) of the 2nd and 3rd arches. 



Gadow regards the auditory ossicles as derivatives of the upper 

 or hyomandibular segment of the 2nd arch (Fig. 10D). 



It will be seen later that the tongue arises from the floor of 

 the pharynx in the field between the 2nd and 3rd arches. 

 The skeletal bases of the ventral parts of the 2nd and 3rd 



