388 



DIGESTIVE SYSTEM OF THE HORSE 



M.S 



M. 2 



;,/. 1 



latiniis) is a small tube of mucous membrane which extends very obliquely through 

 the palatine fissure. Its ventral or palatine end is blind and lies in the submucous 

 tissue of the palate. The dorsal or nasal end communicates with the nasal cavity 

 (in common with the vomero-nasal organ) by a slit-like opening in the anterior 

 part of the "V'entral nasal meatus. 



Vessels and Nerves. — The blood-supply is derived chiefly from the palatine 



arteries and the veins go to the vena re- 

 flexa. The nerves come from the tri- 

 geminus. 



The soft palate (Palatum molle) 

 is a musculo-membranous curtain 

 which separates the cavity of the 

 mouth from that of the pharynx, except 

 during swallowing. It slopes down- 

 ward and backward from its junction 

 with the hard palate. The oral surface 

 faces ventrally and somewhat forward, 

 and is covered with a mucous mem- 

 brane continuous with that of the hard 

 palate. It presents a rounded, median 

 ridge, flanked usually by a sagittal fold 

 on either side. Numerous small ducts 

 of the palatine glands open on this sur- 

 face. On each side a short, thick fold 

 passes to the lateral border of the 

 tongue; this is the anterior pillar of 

 the soft palate (Arcus glossopalatinus) . 

 The pharjmgeal surface faces dorsally 

 and a little backward and is covered by 

 a mucous membrane continuous with 

 that of the nasal cavity. The free bor- 

 der (Arcus palatinus) is concave and 

 thin; it is in contact (except during deg- 

 lutition) with the epiglottis. It is con- 

 tinued by a fold of the mucous mem- 

 brane, which passes on each side along 

 the lower part of the lateral wall of the 

 pharynx and unites with the opposite 

 fold over the beginning of the oesopha- 

 gus; this fold is termed the posterior 

 pillar of the soft palate (Arcus pharyn- 

 gopalatinus). The space between the 

 diverging anterior and posterior pillars 

 (Sinus tonsillaris) is occupied by the 

 tonsil (Tonsilla palatina) . In the horse, 

 however, there is not a compact tonsil, 

 as in man, clog, etc., but a series of 

 masses of lymphoid tissue and mucous 

 glands which extend backward from 

 the root of the tongue on either side a distance of about four inches (ca. 10 cm.). 

 These cause elevations of the surface, on which there are depressions (crypts) in 

 which the gland ducts open. The soft palate is greatly developed in equidffi, its 

 average length, measured mediall.y, being about six inches (15 cm.) . Its length and 

 contact with the epiglottis may account for the fact that in these animals mouth- 



Fig. 329. — Hard Palate and Ad.tacent Part of Soft 

 Palate of Horse. 

 1, Raph6 of palate; 2, ridges of palate; 3, soft palate; 

 7. 1, I. -3, first and second incisor; Di. 3, deciduous third 

 incisor; P. I-4, premolars; M. 1-3, molars. 



