76 TOPOGRAPHICAL ANATOMY OF THE 



the soft palate. The medial lamina is that part of the cartilage which 

 widens towards the pharyngeal ostium, and it is this that constitutes 

 the basis of the broad, valve-like projection at the ostium. For a short 

 distance close to the temporal bone the edges of the laminse are united 

 by fibrous tissue ; but for the greater part they are separated by the 

 elongated slit through which the diverticulum is protruded. Because 

 of the disposition of the cartilage, the lumen of the tube is slit-like in 

 transverse section, and its calibre increases from the tympanic to the 

 pharyngeal ostium. 



The soft palate (Palatum molle). — The soft palate is a long 

 (about 15 cm.) and broad, movable partition between the mouth and the 

 pharynx. One border is attached to the posterior margin of the bony 

 palate ; while the other border is free and gently concave (arcus 

 palatinus). When the soft palate is at rest, its free border is in contact 

 with the glosso-epiglottic fold of mucous membrane, and is overlapped 

 by the curved free part of the epiglottis. 



The lateral borders of the soft palate are connected with the 

 palatine and pterygoid bones. The dorsal oi- pharyngeal surface forms 

 a slightly curved and oblique continuation of the door of the nose. 

 The ventral or oral surface, which is continuous with the hard palate, 

 is slightly concave and in contact with the posterior part of the tongue, 

 and is longitudinally folded. 



Prolongations of the mucous membrane of the soft palate are con- 

 tinuous with the tongue and the wall of the pharynx in the form of 

 folds known as the glosso-j^datiiie and i^haryngo-'palatine arches 

 (arcus glossopalatinus et arcus pharyngopalatinus). The glosso-palatine 

 arch is a thick fold that passes from the lateral border of the tongue to 

 the lateral part of the oral surface of the soft palate, and lies slightly 

 behind the last cheek-tooth. The pharyngo-palatine arch is a 

 prominent fold, continuous with the free border of the soft palate, and 

 sweeps backwards along the lateral wall of the pharynx to unite with its 

 fellow immediately dorsal to the opening into the oesophagus. In the 

 angle of divergence of the two arches is the tonsillar sinus (sinus 

 tonsillaris) in which the flattened palatine tonsil (tonsilla palatina) — 

 a collection of lymphoid nodules and mucous glands — is readily dis- 

 tinguished because of the presence of small flattened elevations and 

 numerous tonsillar crypts. In the horse, the tonsil is not sharply 

 defined, as it is in the dog, but extends beyond the proper limits of the 

 tonsillar sinus and is diffused over the jjosterior part of the tongue 

 (lingual tonsil). 



Structurally the soft palate may be described as composed of four 



