The cavity of the rumen is partially divided into dorsal and ventral
sacs by the =pillars=; these are folds of the wall, strengthened by
additional muscular fibers, and correspond with the grooves on the
outside. The two most extensive ones project like shelves into the
anterior and posterior ends of the cavity forming the blind sacs at
either extremity; they are termed the =chief pillars=. The =anterior
chief pillar= (Pila cranialis) projects obliquely backward and upward
from the ventral wall, and has a thick concave free edge which is
opposite to the tenth and eleventh ribs. Its width from the middle of
the free edge to its anterior border is about eight to ten inches (ca.
20 to 25 cm.). It is continued on either side by the relatively narrow
=longitudinal pillars=, which connect it with the posterior pillar. The
=posterior pillar= (Pila caudalis) is more nearly horizontal than the
anterior one, and separates the large dorsal and ventral posterior blind
sacs. Its concave free border is about a hand’s breadth in front of a
transverse plane through the external angles of the ilia. From it are
detached three =accessory pillars= on either side; of these, two pass
around the blind sacs to meet the corresponding pillars of the opposite
side. They thus mark off the posterior blind sacs from the general
cavity, and are termed the =coronary pillars=. It will be noticed that
the ventral coronary pillar is complete, while the dorsal one is not.
The other accessory pillars join the right and left longitudinal
pillars. The =right longitudinal pillar= is in part double; its ventral
division fades out about the middle of the surface, while the dorsal one
joins the posterior chief pillar. The distance between the middles of
the anterior and posterior pillars is =only= about sixteen to eighteen
inches (ca. 40 to 45 cm.) in a cow of medium size. In this space the
dorsal and ventral sacs communicate freely.
The anterior =dorsal blind sac= of the rumen is separated from the
reticulum by an almost vertical fold formed by the apposition of the
walls of the two compartments. This =rumino-reticular fold= (Pila
rumino-reticularis) is opposite to the seventh rib and intercostal
space. Its free upper edge is concave and forms the lower and outer
margin of the large, oval =rumino-reticular orifice= (Ostium
ruminoreticulare). The inner margin of the fold if continued would end
about at the cardia, but there is in this region no demarcation between
rumen and reticulum; hence it is termed the =atrium ventriculi= or
=vestibule=.
If the rumino-reticular fold and an imaginary completion of it be
taken as the boundary between the rumen and reticulum, it will be seen
that the cardia belongs to the latter. The outer border of the
rumino-reticular fold ends above and behind the cardia, the inner one
just behind the œsophageal groove and about four to five inches lower
down. Undoubtedly food or water swallowed with a moderate degree of
force passes first into the rumen. Foreign bodies (which are commonly
swallowed by cattle) are, however, found in the reticulum.
The =cardiac orifice= is opposite the seventh rib, a little to the left
of the median plane and about four inches (ca. 10 cm.) below the spine;
it is not funnel-shaped.
The =mucous membrane= of the rumen is brown in color, except on the
margins of the pillars, where it is pale. It is for the most part
thickly studded with large papillæ, many of which are nearly half an
inch (ca. 1 cm.) long. The edges of the chief pillars and a large part
of the wall of the middle of the dorsal sac are, however, not
papillated. The papillary arrangement is most marked in the blind sacs.
The papillæ vary much in size and form; the largest are foliate, many
are narrow or filiform, and others are conical or club-shaped. The
mucous membrane on the inner wall of the atrium is finely wrinkled and
non-papillated, while above and externally it is papillated. The
papillary arrangement also extends over the edge of the rumino-reticular
fold an inch or two (ca. 2 to 5 cm.).
[Illustration:
FIG. 289.—THORACIC AND ANTERIOR ABDOMINAL VISCERA OF OX, DEEP
DISSECTION.
Most of the rumen has been removed and the left wall of the reticulum
cut away. _A._, Left pulmonary artery; _B._, left bronchus; _V. V.
V._, pulmonary veins; _b. b._, bronchial lymph glands; _L.g._,
posterior mediastinal lymph gland; _D._, termination of duodenum;
_F._, rumino-reticular fold.
]
The =œsophageal groove= (Sulcus œsophageus) is a semicanal which begins
at the cardia and passes downward (ventrally) on the right wall of the
reticulum to end at the reticulo-omasal orifice. It is about six or
seven inches (ca. 15 to 18 cm.) in length. Its axial direction is
practically vertical, but it is twisted in a spiral fashion; thus its
thickened edges or lips project first backward, then to the left, and
finally forward. The twist involves chiefly the left lip, and the
relative positions of the lips is reversed at the ventral end.
The mucous membrane on the lips of the œsophageal groove is brown and
wrinkled, like that of the atrium; in the bottom of the groove it is
pale, like that of the œsophagus, marked by longitudinal folds, and
presents pointed horny papillæ on the lower part.
The =reticulo-omasal orifice= (Ostium reticulo-omasicum) is situated in
the right wall of the reticulum about five or six inches above the
bottom of the latter. It is rounded, and is limited below and laterally
by the junction of the lips of the œsophageal groove.
In the reticulum the mucous membrane is raised into folds about half an
inch high, which inclose four-, five-, or six-sided spaces (Cellulæ
reticuli); this peculiar arrangement suggested the scientific name, and
also the popular term “honeycomb.” These cells are subdivided by smaller
folds, and the bottoms are studded with pointed horny papillæ. The cells
grow smaller and gradually disappear near the œsophageal groove and the
edge of the rumino-reticular fold; an inch or two from the latter the
mucous membrane has the papillary arrangement of the rumen. At the
reticulo-omasal orifice there are peculiar horny papillæ, which are
curved and resemble the claws of a small bird.
[Illustration: