COMPARATIVE ANATOMY 49 



The sublingual, a small gland, lies close to the submaxillary and 

 along its duct. The duct of the sublingual parallels that of the 

 submaxillary and opens with it. 



Thyroid Glands. — Expose the proximal end of the trachea 

 by removing the superficial muscles of the front of the neck. 

 The thyroid glands will appear as dark colored bodies on either 

 side of the trachea. The thyroids are endocrine glands and 

 have nothing to do with digestive or respiratory systems. 



On each side of the trachea and extending parallel to It are 

 the vagus (tenth cranial) nerve, the common carotid artery carrying 

 blood to the head, and the internal jugular vein returning blood 

 from the brain. Behind the trachea lies the oesophagus. 



With bone forceps cut through the mandible on each side 

 behind the corners of the mouth. Continue the cut along one 

 side of the neck until the first rib Is reached. Lay back the jaw 

 so as to expose the structures of the mouth and pharynx. 



Tongue. ^ — It Is a muscular organ attached at its posterior 

 end. The dorsal surface contains papillae of four kinds: (a) 

 filiform, numerous, simple, and sharp pointed; (b) fungiform, 

 enlarged at the tips and scattered over the middle of the tongue; 

 (c) fiat, numerous on the sides of the base of the tongue; (d) 

 circumvallate, blunt and surrounded by a trench. These last 

 are not numerous; when distinct they are arranged In a V near 

 the base of the tongue. 



Pharynx. — The curtain-like structure on the roof of the 

 mouth is the soft palate. Embedded In pockets at the ventral 

 end of the soft palate on each side are the tonsils. Dorsal to 

 the soft palate and communicating with the nasal cavities by 

 means of the choanae, Is the nasopharynx. Cut along the roof 

 of the mouth and pull aside the soft palate; find the openings 

 of the Eustachian tubes in the dorsal wall of the nasopharynx. 



Larynx and Trachea. — These constitute the "wind pipe." 

 The walls of the trachea are supported by cartilaginous rings 

 that are Incomplete on the dorsal side. The larynx is the 

 enlarged upper end of the wind pipe. Its skeletal parts consist 

 of several cartilages, the largest of which is the thyroid cartilage 

 (Adam's apple of man). The slit-like opening of the larynx 

 is the glottis which Is protected from food particles by a carti- 

 laginous flap, the epiglottis, Immediately In front of It. 



