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 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.
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 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.
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.
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.
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.
It is only in herbivorous mammals that the caecum is developed to this great extent, and among these there is a complementary relationship between the size and complexity of the organ and that of the stomach.
(ab or the horse and the dog may be cited as instances where the single caecum is of large size, this being especially the case of the former, where it is of enormous dimensions; in human beings, on the other hand, the caecum is rudimentary, and best known in connexion with " appendicitis."