THE HEAD. 375 



5. The posterior nasal chamber lies above the soft palate, 



which separates it from the buccal cavity. 



Lay open the nasal chamber by slitting up. the soft palate 

 along the median line, from behind forwards. 



a. The orifices of the Eustachian tubes are a pair of 



oval apertures at the sides of the roof of the 

 chamber, about the middle of its length. 



The Eustachian tubes connect the tympanic 

 cavities with the posterior nasal chamber. The 

 tympano-Eustachian passage is the modified 

 hyomandibular pouch of the embryo, corre- 

 sponding to the spiracle of the dog-fish. Its 

 connection with the ear is purely secondary, the 

 passage serving to keep the pressures of air on 

 the two sides of the tympanic membrane equal. 



Pass a seeker backwards and outivards, along one of the 

 Eii,stachian tubes, into the tympanic cavity. (Cf. fig. 64.) 



b. The organs of Jacobson are a pair of small tubular 



bodies enclosed in the palatal processes of the 

 premaxillse, and lying in the floor of the anterior 

 part of the nasal cavities. Each commilnicates 

 in front with the nostril, and through the naso- 

 palatine canal with the mouth. 



Cut away ivith bone forceps the left side of the nasal 

 chamber from behind fonoards, so as to lay the cavity com- 

 pletely open. Remove the mesethmoid cartilage, and note the 

 arrangement of the turbinal bones, and the relations of Jacob- 

 son's organs. 



6. The salivary glands are large and paired. 



Dissect from the right side. 



The parotid gland, the largest of the salivary 

 glands, is a soft pinkish mass lying in front of 

 and below the external auditory meatus, between 

 this and the hinder edge of the mandible. It is 

 very variable'in size, and may extend beyond the 



