194 THE HEAD AND NECK 



tuberculum impar in the region of the third arch. From this 

 the posterior third (or pharyngeal portion) of the tongue is 

 developed; and it soon unites with the rest of the organ. The 

 sensory nerve-supply of the tongue indicates the complexity of 

 its origin. 



The anterior two-thirds are supplied with ordinary sensation 

 by the lingual and with special sense (taste) by the chorda tym- 

 pani, i.e. by branches from the nerves of the first two arches. 

 The posterior third is supplied by the nerve of the third arch, 

 viz. the glosso-pharyngeal. 



The Nose and Air Sinuses. The development of the 

 nose has already been outlined on p. 191 . The lateral wall of the 

 nasal cavity bears the three conchce (turbinated bones), which 

 project medially and downwards so as to separate the three 

 meatuses of the nose. The mucous membrane on the lateral wall 

 is provided with a freely distensible submucous layer, so that 

 such conditions as hypertrophic rhinitis can readily occur. Over 

 the septum, which forms the medial wall of the cavity, the 

 mucous membrane is firmly bound down. The nerves of 

 ordinary sensation are all derived from the spheno-palatine 

 (Meckel's) ganglion, except the nasal branch, from the ophthal- 

 mic, which ramifies on the septum. The olfactory nerves are 

 distributed to the mucous membrane in the upper third of the 

 cavity. 



Into the forepart of the Inferior Meatus the naso-lacrimal 

 duct opens under cover of the inferior concha. The Middle 

 Meatus receives the openings of the infundibulum from the 

 frontal air sinus, the anterior and middle ethmoidal cells, and the 

 maxillary sinus (antrum of Highmore) (Fig. 57). The two 

 former open into the hiatus semilunaris, a curved depression on 

 the lateral wall. The bulla ethmoidalis, which forms a part of 

 the ethmoid bone, projects into the middle meatus immediately 

 above the hiatus. It contains the middle ethmoidal cells, 

 which open at its upper border. The Superior Meatus receives 

 the posterior ethmoidal air-cells ; the sphenoidal air-cells open 

 into a small depression lying above and behind the superior 

 concha, termed the recessus spheno-ethmoidalis. 



The Nasal Septum is formed posteriorly by the vomer, 

 antero-superiorly by the perpendicular plate of the ethmoid, 

 and antero-inferiorly by the septal cartilage. Deviation of the 

 Septum rarely occurs before the seventh year. It may involve 

 the cartilage only, or both bones and cartilage may be deviated 



