BUCCAL CAVITY 311 



Lay open the nasal chamber by slitting up the soft palate 

 in 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 

 hyo-mandibular cleft of the embryo, corres- 

 ponding to the spiracle of the dog-fish. Its con- 

 nection with the ear is of a purely secondary 

 character, and it forms no part of the essential 

 organ of hearing. 

 Pass a seeker backwards and outwards, along one of the 

 Eustachian tubes, into the tympanic cavity. 



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



enclosed in cartilage, and lying in the floor of 

 the anterior part of the nasal cavity. Each com- 

 municates in front with the mouth by the naso 

 palatine canal, and with the nostril by a more 

 dorsally placed opening. 



Gut away with bone-forceps the left side of the nasal 

 chamber, so as to lay open the cavity completely. Bemove the 

 mesethmoid cartilage, and note the arrangement of the tur- 

 binal bones, and the relations of Jacobson's organs. 



6. The salivary glands are large and paired. 



Dissect from the left side. 



a. 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. 



The duct of the parotid, or Stenonian duct. 

 leaves the gland at its anterior border, and runs 

 forwards just beneath the skin, parallel to and 

 about a quarter of an inch below the zygomatic 

 arch. It opens into the mouth by a small aper- 



