The section passes through the base of the external ear and just
behind the posterior border of the lower jaw. _1_, Rectus capitis
anterior minor; _2_, rectus capitis anterior major; _3_, inner walls
of guttural pouches in apposition; _4_, _4_, arytenoid cartilage,
upper piece apex; _5_, posterior pillar of soft palate; _6_, false
vocal cord; _7_, lateral ventricle of larynx; _8_, true vocal cord;
_9_, vocal muscle; _10_, thyro-hyoideus muscle.
]
It is worthy of note that the pharyngeal orifice of the Eustachian
tube is at such a level as to provide (in the ordinary position of the
head) only an overflow outlet for the escape of fluid which may
accumulate in the pouch. The two pouches are often unequal in size,
and variations in regard to the distance which they extend backward
are not uncommon. In one case, a small aged horse, the right pouch
extended along the œsophagus about five inches (ca. 12 cm.) behind the
ventral tubercle of the atlas, and the left one a little more than two
inches (ca. 6 cm.). No pathological changes were apparent, and the
condition was not recognizable externally. Cases of extreme
size—so-called tympanites—of the pouches occur, and are apparently
congenital defects. In a case in a yearling colt, the head of which
was 24 inches long, the left pouch extended about 12 inches (ca. 30
cm.) behind the tubercle of the atlas, and had a capacity of six
quarts. The anterior end formed a cul-de-sac about two inches (ca. 5
cm.) long between the Eustachian tube and levator palati internally
and the internal pterygoid muscle externally.