THE MOUTH 



333 



downward and forward, and is covered with a mucous membrane continuous with 

 that of the hard palate. It is corrugated and presents numerous small orifices 

 (of gland-ducts) and two sagittal ridges. On each side a short, thick fold passes 

 to join the base of the tongue; this is the anterior pillar of the soft palate (Arcus 

 glossopalatinus). The pharyngeal surface looks upward and backward and is 

 covered by a mucous meml)rane continuous with that of the nasal cavity. The 

 free border (Arcus palatinus) is concave and thin; it is in contact (except during 

 deglutition) with the epiglottis. It is continuous with a fold of the mucous mem- 

 brane, which passes on each side along the lateral 

 Avail of the pharynx and unites with its fellow 

 over the beginning of the oesophagus; this fold 

 is termed the posterior pillar of the soft palate 

 (Arcus pharyngoi)alatinus). The space betw^een 

 the diverging anterior and posterior pillars (Sinus 

 tonsillaris) is occupied by the faucial tonsil. In 

 the horse, however, there is not a compact tonsil, 

 as in man, dog, etc., but a somewhat extended 

 group of mucous glands and masses of lymphoid 

 tissue. These cause elevations of the surface, on 

 which are seen numerous depressions (cryj)ts) in 

 which the gland-ducts open. The soft palate is 

 greatly developed in equida\ its length being five 

 to six inches (12 to lo cm.). Its length and con- 

 tact with the epiglottis account for the fact that 

 in these animals mouth-breathing does not occur 

 under normal conditions, and that in vomiting the 

 ejected matter escapes usually thi'ough the nasal 

 cavity.' 



Structure. — The soft palate consists of: (1) 

 The oral mucous membrane, continuous with that 

 of the hard palate; (2) the palatine glands (Glan- 

 dulse palatinse), which form a layer about half an 

 inch in thickness; (3) the aponeurotic and mus- 

 cular layer; (4) the pharyngeal mucous mem- 

 brane, continuous with that of the nasal cavity. 



The muscles proper to the soft palate are the 

 azygos uvulae, the levator palati, and the tensor 

 palati. 



The azygos uvulae (M. palatinus) consists of 

 two small muscular bundles w^hich lie together 

 at the median line. It is attached through the 

 medium of the palatine aponeurosis to the pala- 

 tine arch, and terminates near the free edge of 

 the soft palate. Its action is to shorten and 

 raise the soft palate. 



The levator palati (M. levator veli palatini) arises from the muscular process 

 of the petrous temporal bone and from the Eustachian tube, and passes forw^ard 

 and downward externally to the latter, to spread out on the pharyngeal surface 

 of the soft palate. It raises the soft palate, thus closing the posterior nares 

 during deglutition. 



The tensor palati (M. tensor veli palatini) is larger than the levator, and is 

 fusiform and flattened. It arises from the muscular process of the petrous tem- 

 poral bone and the Eustachian tube, and passes forward external to the levator. 

 ^ The epiglottis may be either in front of or behind the soft palate; most often it is prevelar. 



Fig. 239. — Hard Palate and Part of 

 Soft Palate of Horse. 

 /, Raphe palati; ;?,'ridges of palate; 

 3, anterior end of soft palate, showing ori- 

 fices of ducts of palatine glands. 



