THE ORAL CAVITY 311 



laryngeal portion (pars laryngea), not well-defined, con- 

 tains the aperture of the larynx, the aditus laryngis. 

 In the oral cavity: 



(a) The hard palate (palatum durum) forms the anterior 

 portion of the roof; its mucous membrane is thrown into 

 a series of transverse ridges. 



(b) The soft palate (palatum molle) is the thin, narrow, pos- 

 terior, membranous portion of the roof. It is very long 

 in the rabbit, extending from the bony palatine bridge 

 backward to a point above the laryngeal aperture, where 

 it ends with a concave free margin. 



The soft palate contains a system of delicate muscles, including the 

 tensor veli palatini (attached to the anteroventral part of the tympanic 

 bulla and to the median process on the bony palatine bridge), the 

 levator veli palatini (originating on the tympanic bulla and inserted in 

 the free edge of the soft palate), the uvular muscle (origin on the median 

 spine of the palatine bridge, insertion in the middle of the soft palate, 

 underlying the buccal mucous membrane), the pharyngopalatine muscle 

 (scattered fascicles from the dorsal wall of the pharynx spreading 

 through the soft tissue of the palate), and the glossopalatine muscle 

 (a very thin system of fibres curving round from the base of the tongue 

 into the centre of the palate). 



(c) The nasopalatine or incisive ducts (dd. nasopalatini) open 

 by small slits about a millimetre behind the secondary 

 incisors, each opening being covered by a slight projection 

 from its medial margin. The ducts connect the anterior 

 portion of the nasal cavity with the mouth, and a probe 

 may readily be passed backward along them from their 

 oral apertures. 



(d) The tongue (lingua) projects upward and forward from its 

 basal attachments on the hyoid into the floor of the mouth. 

 Its connection with the latter is extended forward in the 

 middle line by a vertical membranous fold, the frenulum 

 linguae. Its dorsal surface is divided into a posterior 

 smooth, hard portion, which forms a considerable rounded 

 elevation, and an anterior softer and rougher portion. 

 Both are covered by closely set fine processes, the papillae 

 operariae, which correspond with the filiform and conical 

 papillae of the human tongue. These are most typically 



