i88 THE HEAD AND NECK 



the tongue, and backwards on the dorsum in the median plane 

 for some distance beyond the disease. The tongue is next drawn 

 forwards from the mouth and split in the median plane. The 

 two incisions in the mucous membrane are united by a transverse 

 cut, and the stylo-glossus is exposed and divided as it enters 

 the postero-lateral aspect of the tongue. The genio-glossus and 

 the hyo-glossus are cut away from their attachments to the 

 hyoid bone, and at this stage the lingual artery (p. 154) is secured. 

 In the removal of the whole tongue by the oral route, it is 

 advantageous to split the organ and take it away in two pieces. 



The Palatine (Faucial) Tonsil lies in the lower part of 

 a triangular depression, the tonsillar sinus, on the lateral wall 

 of the pharynx. The sinus is bounded in front and behind by 

 the palatine arches (pillars of the fauces), which meet above 

 on. the posterior border of the soft palate. The supra-tonsillar 

 fossa is a small depression which is situated above the tonsil in 

 the upper part of the tonsillar sinus. Peri-tonsillar abscess 

 gives rise to a swelling, which may involve the adjoining part of 

 the palate as well as the supra-tonsillar fossa. It should be 

 incised with a guarded knife, and the pus evacuated by Hilton's 

 method. The incision is made at the point where the horizontal 

 line corresponding to the free border of the soft palate meets 

 the vertical line corresponding to the glosso- palatine arch 

 (anterior pillar of the fauces). 



Development. The palatine tonsil does not begin to develop 

 till the fourth month of foetal life, although the tonsillar 

 sinus, which represents a persistent part of the second visceral 

 pouch, appears at a much earlier date. Epithelial buds, which 

 subsequently become the tonsillar crypts, grow out from the 

 mucous membrane on the lateral pharyngeal wall into the sur- 

 rounding mesoderm. The latter becomes converted into 

 lymphoid tissue which forms the greater part of the tonsil. 

 Its growth in a lateral direction is obstructed by the pharyngeal 

 aponeurosis, and so, as the organ grows, it bulges into the oral 

 part of the pharynx. The tonsil, therefore, consists partly of 

 mucous membrane, which covers its medial surface and lines its 

 crypts, and partly of lymphoid tissue. 



The deep surface of the tonsil has no definite capsule, and 

 is only separated from the pharyngeal aponeurosis, which lines 

 the superior constrictor, by loosely arranged areolar tissue. 

 On this account the tonsil can readily be dragged medially from 

 its fossa in the operation of enucleation. Hypertrophy of the 



