1 86 LABORATORY MANUAL FOR VERTEBRATE ANATOMY 



margin may be concealed by a leaf -shaped structure, the epiglottis, which projects 

 from the base of the tongue. If so, the epiglottis should be pressed out of the 

 way.) The opening formed by the free border of the palate is known as the 

 isthmus of the fauces. This opening leads into the cavity of the pharynx. Shortly 

 anterior to the free border of the soft palate on each side is a pit, the tonsillar fossa, 

 which contains a small mass of lymphoid tissue, the palatine tonsil. The tonsillar 

 fossa is bounded in front and behind by low folds, an anterior glossopalatine 

 arch and a posterior pharyngopalatine arch. Now slit the soft palate forward 

 along its median line. A cavity, the nasopharynx, a part of the pharynx, is 

 revealed dorsal to the soft palate. At the anterior end of the nasopharynx 

 are the two posterior nares or choanae, the internal ends of the nasal passages. 

 Posterior to them on the lateral wall of the nasopharynx will be noted a pair of 

 oblique slits; they are the openings of the auditory or Eustachian tubes, canals 

 which connect the pharynx with the cavity of the middle ear. 



The pharynx narrows posteriorly into the esophagus. Anteriorly to the 

 entrance into the esophagus is situated the entrance into the respiratory tract. 

 This entrance is guarded by a projecting process, the epiglottis, which if not 

 already identified will be seen on pulling the tongue well forward. In the 

 pharynx the paths for food and air are crossed (as is the case in all of the air- 

 breathing vertebrates). It will be noted, however, that owing to the formation 

 of the palate and the consequent posterior migration of the posterior nares, 

 the air no longer enters the oral cavity as is the case in Amphibia and most rep- 

 tiles but proceeds directly into the pharynx. 



2. The hyoid apparatus, the larynx, the trachea, and the esophagus. 

 Press the tongue dorsally against the lower jaw and find on its external surface 

 at its base a bone, the body of the hyoid. This is a stout bone in the rabbit, a 

 narrow bar in the cat. Clear away muscles from its surface so as to reveal it 

 and the two horns or cornua which extend from its sides. In the rabbit the 

 horns are short processes which are connected by slender tendinous muscles 

 with the jugular process of the occipital bone. In the cat the anterior horn is 

 long and slender and consists of a chain of four bony pieces, the last of which 

 articulates with the tympanic bulla; the posterior horn is short and is united 

 to the larynx. The hyoid and its horns are derived in mammals from the 

 second and third gill arches. The hyoid supports the base of the tongue and 

 serves for the origin and insertion of muscles. 



In the median ventral line posterior to the body of the hyoid is a chamber 

 with cartilaginous walls, the larynx or voice box, which constitutes the projec- 

 tion in the throat popularly known as Adam's apple. By making a cut through 

 the base of the tongue and gently severing the muscle attachments, the larynx 

 may be freed and lifted forward. At the top of the larynx is a large opening, 

 the glottis, from whose ventral margin the epiglottis projects. Dorsal to the 

 glottis and bound with it by muscles is another opening, generally collapsed and 



