The stomach is simple, and there is no caecum to the intestine, although this is present in the opossums.
Caecum of moderate size.
With one exception, the intestine has a caecum, and the pouch is large and opens forwards.
Caecum very short and wide, with a vermiform appendage (see Wombat).
Caecum very long and dilated, with numerous folds.
Caecum present (except in Tarsipes), and usually large.
From this we pass to a stomach and a coil of intestine embedded in the lobes of a voluminous liver; a caecum of large size is given off near the commencement of the intestine.
Protonemertini, in which there are two layers of dermal muscles, external circular and internal longitudinal; the nervous system lies external to the circular muscles; the mouth lies behind the level of the brain; the proboscis has no stylet; there is no caecum to the intestine.
Heteronemertini, in which the dermal musculature is in three layers, an external longitudinal, a middle circular, an internal longitudinal; the nervous system lies between the first and second of these layers; the outer layer of longitudinal muscles is a new development; there is no intestinal caecum; no stylets on the proboscis and the mouth is behind the level of the brain.
It is at times sacculated, but its chief interest is that, as Lebedinsky 1 has shown, the tip of the caecum in embryonic life opens to the exterior as the blastopore.
The stomach is simple, the caecum large and capacious, the placenta diffused, and the teats inguinal.
It is not a simple diverticulum of the collar-gut, but a complex structure possessing paired lateral pouches and a ventral convexity (ventral caecum) which rests in a concavity at the f_ ont end of the body of the nuchal skeleton (fig.
In all known Pantopoda the size of the body is quite minute as compared with that of the limbs: the alimentary canal sends a long caecum into each leg (cf.
In some of the v, Caecum of stomach.
V, Caecum of stomach.
This latter organ is pigmented in all Polyzoa, and is produced, in the Ectoprocta, beyond the point where the intestine leaves it into a conspicuous caecum (fig.
A pyloric caecum connected with the stomach is commonly found, containing a tough flexible cylinder of transparent cartilaginous appearance, called the " crystalline style " (Mactra).
The radula consists of a chitinous band bearing teeth, secreted by a ventral caecum of the pharnyx and moved by an apparatus of cartilage and muscles.
The teeth are secreted by a small number of cells at the closed end of the caecum, the basal membrane by a transverse row of cells in front of these.
Beneath the anterior parts of the radula where it emerges from the caecum are a pair of cartilages, and attached to these a number of special muscles by which the radula is moved backwards and forwards to act as a rasp. The secretion of the radula at the closed end of the caecum is continuous, so that it is constantly growing forward as fast as its exposed anterior portion is worn away by use, just as a fingernail is pushed forward by constant growth at its posterior end, and is worn away or has to be cut short from time to time at its outer end.
All rodents, with the sole exception of the dormice, have a caecum, often of great length and sacculated,, as in hares, the water-rat and porcupines; and the long colon in some, as the hamster and water-rat, is spirally twisted upon itself near the commencement.
In the soft parts the caecum is very large, the penis is armed with a pair of barbed horny claspers and the scrotum is spiny.
The intestinal canal is long, and has, in addition to the ordinary short, but capacious and sacculated caecum at the commencement of the colon, lower down, a pair of large, conical, pointed caeca.
The digestive tube is straight and simple, wider in its anterior part, into which opens the duct of the hepatic caecum (fig.
A, Edge of groove formed by adhesion of median dorsal surface of alimentary canal to sheath of notochord; b, median dorsal surface of alimentary canal; c, left dorsal aorta; cc, single dorsal aorta, formed by union of the two anterior vessels; cc', same vessel resting on intestine; d, cut edge of pharyngo-pleural folds of atrial tunic, really the original outer body-wall before the downgrowth of epipleura; d', atrial tunic (original body-wall) at non-perforate region, cut and turned back so as to expose peri-enteric coelom and intestine r; e', upstanding folds of body-wall (pharyngo-pleural folds) on alternate bars of perforate region of body; f, atrio-coeiomic canals or brown funnels (collar-pores of Balanoglossus); g, cavity of a gonad-sac; m, cut musculature of body-wall; n, anus; o, post-atrioporal extension of atrial chamber in form of a tubular caecum; p, atriopore; q, hepatic caecum; r, intestine; s, coelom; t, area of adhesion between alimentary canal and sheath of notochord; v, atrial chamber or branchial cavity; w, post-atrioporal portion of intestine; x, canals of metapleura exposed by cutting; E, probe passing through atriopore into atrial or branchial chamber; FF', probe passing from coelom, where it expands behind the atriopore, into narrower perienteric coelom of praeatrioporal region.
A, Cavity surrounding fin ray; a', fin ray; b, muscular tissue of myotome; c, nervecord; d, notochord; c, left aorta; f, thickened ridges of epithelium of praeoral chamber (Rader organ); g, coiled tube lying in a coelomic space on right side of praeoral hood, apparently an artery; h, cuticle of notochord; i, connective-tissue sheath of notochord; k, median ridge of skeletal canal of nerve-cord; 1, skeletal canal protecting nerve-cord; m, inter-segmental skeletal septum of myotome; n, subcutaneous skeletal connective tissue; o, ditto of metapleur (this should be relatively thicker than it is); q, subcutaneous connective tissue of ventral surface of atrial wall (not a canal, as supposed by Stieda and others); r, epiblastic epithelium; s, gonad-sac containing ova; t, pharyngeal bar in section, one of the "tongue" bars alternating with the main bars and devoid of pharyngo-pleural fold and coelom; v, atrio-coelomic funnel; w, socalled "dorsal" coelom; x, lymphatic space or canal of metapleur; y, sub-pharyngeal vascular trunk; z, blood-vessel (portal vein) on wall of hepatic caecum; aa, space of atrial or branchial chamber; bb, ventral groove of pharynx (anteriorly this takes the form of a ridge); cc, hyperbranchial groove of pharynx; dd, lumen or space of hepatic caecum; ee, narrow coelomic space surrounding hepatic caecum; $, lining cell-layer of hepatic caecum; gg, inner face of a pharyngeal bar clothed with hypoblast, the outer face covered with epiblast (represented black); hh, a main pharyngeal bar with projecting pharyngeal fold (on which the reference line rests) in section, showing coelomic space beneath the black epiblast; ii, transverse ventral muscle of epipleura; kk, raphe or plane of fusion of two down-grown epipleura; 11, space and nucleated cells on dorsal face of notochord; mm, similar space and cells on its ventral face.
This is the hepatic caecum (fig.
No food passes into the hepatic caecum, which has been definitely shown on embryological and physiological grounds to be the simplest persistent form of the vertebrate liver.
In general structure they all closely resemble human beings, as in the absence of tails; in their semi-erect position (resting on finger-tips or knuckles); in the shape of vertebral column, sternum and pelvis; in the adaptation of the arms for turning the palm uppermost at will; in the possession of a long vermiform appendix to the short caecum of the intestine; in the size of the cerebral hemispheres and the complexity of their convolutions.
Alimentary canal; in man and mammals divided into the smaller intestine, from the pylorus to the iliocaecal valve, and the larger, reaching from the caecum and colon to the end of the rectum.
The alimentary canal is long, and the caecum well developed.
The stomach is small; into it open a small pyloric caecum and the ducts of the liver, paired in Dentaliidae, one on the left only in Siphonodentalium.