Encyclopaedia Britannica > Volume 3, Anatomy-Astronomy

ANATOMY.
59
Special trunk, protected by those of the locomotive system; and
Anatomy, that they are lined on one side by mucous membrane,
continuous with the external integuments. By means of
this arrangement, which is necessarily allied with their
property of converting foreign into proper matter, all the
entrophic organs, with the exception of the heart, com¬
municate with the surface of the body.
k fourth anatomical character common to these organs
is, that though continuous by their mucous investment
with the outer surface of the body, their opposite, placed
on the outside of the serous membranes, forms shut cavi¬
ties, not communicating, unless in one instance—the peri¬
toneal end of the oviduct in the female—with the external
surface. Whatever be the intermediate substance, these
organs are placed between the mucous and serous mem¬
branes.
The entrophic organs may be distinguished into two
orders, according to the degree of the process performed
by each. The nutritive function consists of two subor¬
dinate functions, the Umitrophic or alimentary, and the
hcematrophic or circulatory; the first the preparation of the
materials destined to be employed in nutrition ; the second
the distribution of these, after preparation, to the different
regions and organs of the system. The organs by which
the first process is accomplished constitute the first order;
those by which the second is effected constitute the
second order.
CHAP. I. THE LIMITROPHIC ORGANS.
The limitrophic organs consist of two divisions ; those
for digestion of the food, or the chylopoietic, and those
for absorption of its nutritious part. The former is ef¬
fected in successive processes in the divisions of the ali¬
mentary canal, a tubular musculo-membranous apparatus,
extending from the mouth to the anus. The second is
accomplished by an assemblage of minute valvular tubes,
the lacteals, terminating in the thoracic duct.
SECT. I. THE ORGANS OF DIGESTION; THE CHYLOPOIETIC
ORGANS.
The organs of mastication have been described already
in the fourth section of the second chapter of Fart First.
The pha- The pharynx, placed on the median line, symmetrical
rvnx. and regular, occupying the upper part of the neck, makes
a close approach to the organs of relation, and marks the
transition from these to those of the entrophic function.
Attached above to the cuneiform process of the occipital
bone, behind to the cervical vertebrae, and with the nostrils,
mouth, and larynx before, it forms an irregular vaulted
apartment about four inches long and two broad at its
widest part, and contracting below, where it is continuous
with the oesophagus. Besides the opening into this tube,
the pharynx presents six apertures ; the pharyngeal aper¬
tures of the nostrils, the pharyngeal orifice of the mouth,
the upper end of the larynx, and the pharyngeal aper¬
tures of the Eustachian tube.
It consists of a mucous membrane stretched over loose
filamentous tissue inclosed by three muscles, the superior,
inferior, and middle constrictor, and attached to the cunei¬
form process, the cervical vertebrse, and the lateral regions
of the neck, by filamentous tissue.
By the superior laryngeal, the pharyngeal, the thyroid,
the lingual, and palatine arteries, it receives blood, which
is returned by a still greater number of veins to the exter¬
nal and internal jugular trunks. The nerves of the pharynx
come from the glosso-pharyngeal, the hypoglossal, the
pneumogastric, and the great sympathetic.
The ceso- 1 he oesophagus(^gula) is a cylindrical musculo-membran-
phagus. ous tube^ communicating above with the pharynx, and
below with the stomach. Placed above between the Special
cervical vertebrae behind and the windpipe before, at the Anatomy,
lower end of the larynx it inclines to the left, returns tov^~^^'
the median line at the sternum, bends again to the left at
the bifurcation of the trachea, and continues on the left
side of the line, passing the aperture of the diaphragm,
near the ninth dorsal vertebra, to its junction with the
stomach. With the vertebral column behind, at its first
inclination it covers the longus colli in the chest, crosses
the vena azygos above, and covers the thoracic duct in the
middle, and the aorta below. With the jugular veins and
carotids on each side in the neck, below it has the trachea
on the right, and the recurrent nerve and common carotid
on the left; and in the chest it has the aorta on the left
and behind. (Plate XXIX. fig. 2, c.)
Lined on the inside by a follicular mucous membrane
which assumes longitudinal folds (plicae), the oesopha¬
gus consists of two ranges of muscular fibres, the one
transverse, the other longitudinal. The first are most
distinct at the pharyngeal end. The second form a mani¬
fest thick layer through the whole extent of the tube.
Externally is a quantity of filamentous tissue, connecting
the tube to that of the mediastinum and adjoining parts.
The oesophagus is supplied with blood from the inferior
thyroid, thymic, laryngeal, pharyngeal; the aorta by pro¬
per oesophageal arteries, the superior intercostals and
bronchials, the pericardial, mediastinal, diaphragmatics,
and even the coronary of the stomach. The blood is
returned by veins equally numerous. The oesophageal
nerves proceed from three different sources. Above, it
receives filaments from the glosso-pharyngeal and pneu¬
mogastric, in the middle from the latter, and below from
the pneumogastric and the great sympathetic.
The stomach (ventriculus) is a large pyriform musculo- The sto-
membranous sac, incurvated on itself (Plate XXIX. fig. 2, mach.
and Plate XXXVI. fig. 4), situate in the epigastric and left
hypochondriac regions, communicating above with tlie oeso¬
phagus, and below with the duodenum. Bounded above
by the diaphragm, and the liver, which covers it, it has the
spleen attached to its left great extremity, the transverse
arch of the colon to the inferior large arch; and its posterior
surface corresponds to the duodenum, pancreas, mesoco¬
lon, and large abdominal vessels.
The pyriform sac of the stomach is distinguished into
a large end or sac (fundus), and a small extremity named
the pyloric; while a particular incurvation of its direction
gives it a large inferior arch (arcus major), and a small
superior arch (arcus minor). At the left extremity of
the latter is the cardia, the orifice by which the oesopha¬
gus enters the stomach (osteum cesophageum); and from
this round the fundus is the large arch. A vertical plane
drawn from the cardia divides the stomach into two por¬
tions,—the cardiac (fundus, saccus ccecus), and pyloric,
terminating in an annular contracted opening, about an
inch broad (pylorus, ostium duodenale sive pyloricum).
Between the two arches is the superior-anterior surface,
covered partly by the left lobe of the liver, partly by the
left rectus and hypochondre, and the inferior-posterior sur¬
face behind.
The stomach consists of peritoneum externally, mucous Structure,
membrane internally, and an intermediate muscular layer
with filamentous tissue.
The peritoneal covering is arranged in a peculiar man¬
ner. The anterior fold, meeting the posterior at the
small arch, joins it, and forms a membranous production
(omentum gastro-hepaticum), connecting the organ to the
inferior surface of the liver, where they again separate to
invest the upper and lower divisions of that organ. T hese
folds, meeting in like manner along the large arch, where
they form similar duplicatures, are again separated to in-