DISSECTION OF THE HEAD AND NECK. 209 



Behind it is bounded by the extreme upper part of the dorsum of the 

 tongue. In the horse, owing to the length of the soft palate, this 

 aperture is closed except during the passage of solids or liquids in 

 deglutition. 



Structure of the Soft Palate. This comprises two layers of mucous 

 membrane, and, included between these, a layer of mucous glands, a 

 fibrous aponeurosis, muscles, vessels, and nerves. 



Mucous Membrane. — The membrane covering the oral aspect of the 

 curtain is directly continuous with that of the hard palate, and through 

 the anterior pillars it is also continuous with the mucous membrane of 

 the tongue. It has a thick tesselated epithelium, and shows numerous 

 small papillae perforated by the ducts of the subjacent glands. The 

 mucous membrane of the pharyngeal surface of the curtain is continuous 

 with that of the nasal chambers, and will be exposed in the dissection of 

 the pharynx. 



Staphyline 1 Mucous Glands. — These form a thick granular layer which 

 will be exposed by removing the mucous membrane from the oral surface 

 of the soft palate. The ducts of the glands open on the oral surface of 

 the curtain, and the bolus of food thus gets a mucous coating as it 

 passes through the isthmus. 



Fibrous Aponeurosis. — If the glandular layer be removed, this will be 

 exposed in the anterior part of the curtain. It is fixed in front to the 

 margin of the hard palate ; and behind it is continuous with the palato- 

 pharyngeus, to which it serves as a tendon of origin. 



Muscles of the Soft Palate : — 



The Palato-glossus Muscle (Plate 32). This muscle has been dis- 

 sected with the tongue (page 205). 



The Palato-Pharyngeus (Plate 32). This muscle will be found 

 beneath the glandular layer in the posterior half of the curtain. At the 

 middle line it is continuous with the opposite muscle, and in front it is 

 continuous with the fibrous aponeurosis. At the side of the soft palate 

 it is continued to the wall of the pharynx ; and, passing beneath the 

 hyo-pharyngeus muscle, it becomes inserted into the edge of the thyroid 

 cartilage. In the latter part of its course it need not be exposed at 

 present. 



Action. — To tense the velum and carry its free edge upwards towards 

 the pharynx. 



The Tensor Palati (Plates 31 and 32). This muscle and the next 

 will be found parallel to the Eustachian tube, and on its outer side. It 

 arises, in common with the levator palati, from the styloid process of the 

 petrous temporal bone, and from the Eustachian tube. Its terminal 



1 Strictly speaking, this adjective applies to structures pertaining to the uvula, but 

 it may conveniently be used to distinguish parts belonging to the soft palate of the 

 horse, in which the uvula is not developed. 



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