Page:Laboratory Manual of the Anatomy of the Rat (Hunt 1924).djvu/85

Rh Papillae cover the dorsal surface of the anterior three- quarters of the tongue, the tip, and dorsal portions of the lateral surfaces. They are entirely lacking on the posterior quarter of the upper surface, ventral portions of the lateral surfaces, and the under side of the free anterior end. The filiform papillae are slender pointed structures with their tips generally directed backward. On the anterior half of the dorsal surface these papillae are rather conspicuous when seen under the dissecting microscope. In a triangular area about half way between the anterior and posterior ends of the tongue the filiform papillae are larger than elsewhere, conical and erect. The filiform papillae back of this area are so numerous and slender that here the tongue has a velvety appearance under the dissecting microscope. A few, low, cylindrical fungiform papillae are scattered over the anterior half of the dorsal surface, chiefly toward the tip.

There is no organized tonsil. This organ is represented merely by scattered follicular openings on the longitudinally folded side walls of the narrow faucial canal.

Exercise XX. Sketch a dorsal view of the tongue.

The soft palate forms the ventral floor of the nasopharynx (pars nasalis). This is a relatively large cavity which opens anteriorly through the single posterior naris into the nasal cavity. Toward its posterior end the nasopharynx curves downward and opens into the pharynx proper. The lateral walls are supported by the sphenoid processes of the palatine bone and the median pterygoid processes of the alisphenoid, while the basisphenoid and presphenoid bones support the roof. The auditory (Eustachian) tubes from the middle ears open into the nasopharynx about half a centimeter from the posterior border of the soft palate. The opening of each tube is a longitudinal slit near the angle between the lateral and dorsal