The frontal sinus, then, occupies all the supero-lateral portion of the cranial box, which is thus provided with a double wall. At one point, however, over a lozenge-shaped area, the cranial cavity is only protected by a single wall. It is in this region that the slaughterman strikes the animal when killing it.
The frontal sinus may be examined by inspection and palpation. Inspection sometimes reveals deformity of the external wall of the sinus. Such deformity, however, is rare, and Moussu has only observed it in two cases of tuberculosis of the bones forming the cranial wall.
By percussion one detects abnormal sensibility, and partial or complete dulness over certain areas.
Fig. 164.—General arrangement of the sinuses. The circular openings indicate points at which trepanation is performed.
Maxillary sinus.—The maxillary sinus occupies the whole lateral region of the face, from the inferior extremity of the maxillary spine as far as the sub-orbito-palatine region. In front its external wall is very solid, but behind, below the orbit, is extremely thin. Externally the sinus is largely protected by the anterior insertion of the external masseter muscle, a fact which explains how rarely it is injured.
Larynx. In consequence of its deep situation, the larynx can scarcely be examined except by inspection, external palpation, internal digital palpation, and auscultation.
External examination presents no difficulty, and enables one to detect lesions around or near the larynx.
Palpation reveals the existence of œdematous swellings, enlargements of the retro-pharyngeal lymphatic glands, inflammatory engorgements, etc.
Internal digital examination, like examination of the pharynx, can only be performed after very firmly fixing the animal in position, and inserting a gag in the mouth.