400 THE DIGESTIVE APPABATUS IN MAMMALIA. 



Structure. — The palate lies on the bony vault formed by the palatine and 

 supermaxillary bones. It includes in its structure : 



1. A fibrous membrane, applied to the bone just mentioned, which sustains 

 a remarkably developed venous network, constituting a veritable erectile tissue, 

 and gives to the palate a greater or less degree of thickness, according to its state 

 of turgescence (Fig, 215, 2). 



2. A mucous layer, extremely adherent, by its deep face, to the preceding 

 tissue, and of a whitish aspect in the horse. The corium, formed entirely of 

 connective tissue, shows numerous conical papillas, especially at the posterior 

 part of the palate. The epithelium fills up the depressions between the papillse ; 

 it is stratified, squamous, and remarkable for the great thickness of its horny 

 layer. 



3. Two voluminous artmes — the palatine — are lodged in the bony fissures of 

 the palatine roof. These arteries proceed parallel to each other, and unite in 

 front by anastomosing to form a single trunk, which enters the incisive foramen. 

 It is of importance to know their disposition, from a surgical point of view, as care 

 ought to be taken not to wound them when abstracting blood from the palate. 

 The blood carried by these arteries arrives in the deep-seated erectile membrane, 

 and is finally removed by two very short venous trunks, which do not pass with 

 the palatine arteries into the palatine canal, but only into the palatine fissure. 



4. Sensory nerves, which accompany the arteries, and are derived from the 

 superior maxillary branch of the fifth pair of cranial nerves. 



Functions. — The palate has a passive, but important, share in mastication 

 and deglutition ; furnishing the tongue, as it does, with a firm basis in the 

 movements it executes when passing the food between the molar teeth, and in 

 carrying the ahmentary mass backwards to the pharynx. 



4. The Tongue (Figs. 221, 223, 251, 306). 



Preparation. — 1. By means of a strong saw without a back, make an antero-posterior and 

 vertical section of the head, in order to study the general disposition of the tongue. 2. From 

 another head remove the lower jaw, leaving the tongue in the intermaxillary space, to examine 

 the external conformation of the organ (see the dissection of the palate). On a third head, 

 kept for the study of the muscles, these parts are exposed in the following manner : The 

 masseter is entirely removed, and the cheek is detached from the lower jaw and turned over 

 on the upper jaw ; then the branch of the inferior maxilla is sawn through transversely, at 

 first behind, next in front of the molar teeth : the upper piece of bone should be detached by 

 disjointing it behind the temporo-maxillary articulation, after destroying the capsular liga- 

 ment and dividing the insertions of the pterygoid muscles. With resrard to the inferior piece, 

 it is reversed in such a way as to put the line of the molars downwards, and the inferior border 

 of the bone upwards in the bottom of the intermaxillary space. To do this, it is sufficient to 

 separate the buccal mucous membrane from the mylo-hyoideus muscle, proceeding from above 

 to below. Tiie dissection thus prepared, serves not only for the study of the muscles of the 

 tongue, but also for those of the deep salivary glands, the pharynx, larynx, guttural pouches, 

 the nerves and arteries of the head, etc. It is always better, in order to facilitate this dissec- 

 tion, to keep the jaws apart by fixing a piece of wood or bone between the incisor teeth 

 immediately after the death of the animal. 



llie lingual canal. — The inferior wall (or floor) of the mouth, circumscribed 

 by the lower alveolar arches, forms an elongated cavity named the lingual canal 

 (or space), which lodges the organ designated the tongue. This canal occupies, 

 in its anterior third, the superior surface of the body of the inferior maxilla. For 

 the remainder of its extent, it is formed by a double groove in the floor of the 

 mouth, at the sides of the tongue. It exhibits the suhlimiiutl crest oxi^ the barhs^ 

 of which we will speak when describing the sublingual and maxillary glands. 



