The Ear

The external ear differs greatly in size and form in the various breeds; in most it is relatively wide and thin and the greater part of it hangs down over the opening. The anterior border has a prominence (Spina helicis) at its lower part, and below this it divides into two branches (Crura helicis). One of these continues down to a blunt point, while the other turns in to the cavity of the concha. The posterior border forms a pouch below its middle, and is thick and rounded in its basal part. Here the conchal cartilage bears a pointed process (Processus uncinatus), which projects upward and backward. The outer wall of the cavum conchæ is supported by a quadrilateral plate (Tragus) above and a semiannular cartilage below. The concave surface presents several cutaneous folds, and in the cavum conchæ there are ridges and irregular prominences. There are long hairs on the borders, apex, and the folds of the concave surface, but the skin of the cavum conchæ is bare. The annular cartilage is a complete ring. The osseous external auditory meatus is wide and extremely short.

The auricular muscles are thin. The scutularis is extensive and is divisible into interscutularis and fronto-scutularis. It partly covers the occipitalis muscle, which is oval and unpaired and ends in the fascia of the frontal region. The scutulo-auriculares superficiales, inferior et accessorius, and the cervico-scutularis are not differentiated as separate muscles. The cervico-auricularis superficialis and the parieto-auricularis both bifurcate and are inserted into the base of the concha and the scutiform cartilage. The parotido-auricularis is narrow and almost long enough to meet the opposite muscle. The tragicus consists of two parts; of these the lateral one is long and arises from the border of the mandible above the angular process. The helicis and the verticalis auriculæ are well developed.

The tympanic cavity is very roomy, extending ventrally into the large but simple cavity of the bulla ossea. The tympanic membrane is extensive and oval. The promontory is very pronounced. The auditory ossicles are large. The Eustachian tube is short, and has a fibrous outer wall. Its pharyngeal opening is an oblique slit situated on the lateral wall of the naso-pharyngeal meatus, and is margined internally by a thick mucous fold.

The cochlea has three and a half turns and is more sharply pointed than in the ungulates.