M. levator veli palatini ([Fig. 66], e, e′).—A flat triangular muscle which lies within the tensor.
Origin from the surface of the body of the sphenoid mediad of the groove for the Eustachian tube, from the styliform process of the bulla tympani, and in part from the Eustachian tube. The muscle passes caudad, and its fibres then diverge into the velum palatinum.
Insertion into the velum palatinum, some of the fibres meeting in the middle line.
Action indicated by the name.
A number of other muscles have been [described] in the soft palate of the cat; they are, however, poorly developed and not easily distinguished. For an account of these, see Stowell, Proceedings of the Am. Soc. of Microscopists, 1889.
2. The Pharynx.
—At the caudal end of the mouth cavity the passage for the food and that for the air cross; at the cranial end the food-passage (mouth) is ventral, the respiratory passage (nasal cavity) dorsal. Farther caudad the food-passage (œsophagus) is dorsal, while the respiratory passage (larynx and trachea) is ventral. In the region of crossing there is therefore for a certain distance a common passageway for food and air, and this is known as the pharynx. It extends from the isthmus faucium, at the free caudal margin of the soft palate, to the beginning of the œsophagus, at the dorsal or caudal margin of the opening of the larynx. The dorsal wall of the pharynx is separated from the base of the skull and the centra of the cervical vertebræ only by intervening muscles (longus capitis, levator scapulæ ventralis, and longus colli, [Fig. 72], [page 143]). Its lateral and ventral walls are supported by the hyoid bone and the cartilages of the larynx.
Craniad the pharynx continues, usually, without break into the cavity lying dorsad of the soft palate. But at the time of swallowing the free edge of the soft palate is pushed dorsad against the dorsal wall of the pharynx, while the caudal part of the pharynx is drawn craniad, so as to form a cavity continuous with that of the mouth. In this way the cavity above the soft palate is completely separated at the time of swallowing from the rest of the pharynx. This separated portion is known as the nasopharynx: it is strictly a portion of the respiratory passage, as the food does not pass into it. The nasopharynx is continuous craniad by the choanæ with the nasal cavity; it forms a horizontal tube between and ventrad of the perpendicular plates of the palatine bones, and has the same craniocaudal extent as the soft palate. Its dorsal wall lies against the basis cranii and the longus capitis muscles; its lateral walls against the pterygoid muscles and the perpendicular plates of the palatine bones; its ventral wall is the soft palate. At the middle of its length, at the junction of its dorsal and lateral wall, are two longitudinal slits about three millimeters long. These are the medial openings of the Eustachian tubes, by which the nasopharynx communicates with the tympanic cavity.
The pharynx proper, situated caudad of the nasopharynx, is smaller than the latter. It is bounded craniad by the epiglottis and the margin of the soft palate, and is continuous between the two, by the isthmus faucium, with the mouth cavity. Its floor is formed by the cranial end of the larynx. At its caudal end it passes dorsally into the œsophagus, while ventrally it communicates with the larynx. Its walls are muscular.