THE HEAD AND NECK 



muscle is derived from the fourth arch, and is supplied by the 

 external branch of the superior laryngeal, which is the nerve of 

 that arch. The muscle masses of the fifth and sixth arches form 

 the intrinsic muscles of the larynx, which are supplied by the 

 recurrent (laryngeal) nerve the nerve of these arches. Of the 

 visceral clefts all but the first, which forms the external acoustic 

 meatus, disappear entirely. The first visceral pouch forms the 

 tympanum and the auditory (Eustachian) tube,, so that the 

 tympanic membrane occupies the site of the cleft membrane. 

 Remains of the second pouch form the supra-tonsillar fossa 

 (p. 1 88) and the pharyngeal recess (of Rosenmiiller) (p. 190). 



1st Branchial 

 cleft 



2nd Branchial 

 pouch 



2nd Branchial . 

 cleft 



3rd Branchial 

 jx>uch 



4th Bran 



pouch 



4th Branchial .."T 

 cleft 



Separating membrane / / 

 1st cleft = tympanum i'/ 

 and tube ' ' / 



5th Branchial pouch 



FIG. 46. Scheme showing the Branchial Pouches, Clefts and Arches 

 and some of their derivatives. 



The upper two branchial arches develop much more rapidly 

 than the lower arches, which are soon overlapped and hidden 

 by the second. The ectodermal covering of the second arch 

 comes into contact and fuses with the ectoderm caudal to the 

 fourth cleft. In this way the second, third, and fourth clefts 

 no longer open on the surface, but instead they open into a 

 common space termed the cervical sinus. This enclosed ecto- 

 derm normally disappears, but the persistence of any part of it 

 may lead to the formation of branchial cysts or fistulse. 



A Blind External Branchial Fistula is the most frequent 

 deformity arising from persistence of the ectoderm which lines 

 the cervical sinus and normally disappears. It is met with 

 usually near the anterior border of the sterno-mastoid, but the 



