The dogfish usually furnished for dissection are immature, having the genital glands and ducts only partly developed. In mature females the oviducts are conspicuous tubes ventral to the kidneys. In young specimens they appear as slender, white tubes extending along the inner borders of the kidneys. Anteriorly, the oviducts pass ventrad over the front of the liver to the ventral wall of the body; at the same time they unite to form a funnel, the ostium tubae, which opens into the coelom. Vestigial oviducts opening into the coelom are found in the same position in males.
In males, the vasa deferentia appear as slender, irregularly coiled white tubules lying near the medial border of the kidneys; they are much less conspicuous than the oviducts, especially in young males.
The alimentary system. In dissecting the following organs, care should be taken not to break the connections of the organs with each other or with other parts, or to cut blood vessels. Organs should not be removed until such procedure is directed.
The mouth and pharynx can be studied to better advantage later with the dissection of portions of the vascular system.
The oesophagus can be seen above the liver, by pressing that organ aside, as a somewhat constricted tube entering the anterior end of the abdominal cavity. It immediately joins the stomach, which is more or less expanded according to the amount of food contained in it.
The stomach passes directly back for more than half of the length of the abdominal cavity, then turns abruptly forward, forming a distal limb about a third as long as the proximal. (Two-thirds to three-quarters as long in Eugaleus.) The distal limb ends with a sharp turn to the right, where it is constricted by the pyloric sphincter, which marks the end of the stomach.
The narrow beginning of the intestine forming the turn to the right and backward is frequently distinguished as the duodenum. It leads from the stomach directly into the large intestine, a wide, straight tube marked externally by a spiral line of several turns. The large intestine narrows posteriorly, forming a region somewhat arbitrarily termed the rectum, which opens into the cloaca through the anus.
Dorsal to the rectum and attached to that body is a narrow spindle-shaped body, the rectal or digitiform gland.
The liver is attached to the anterior wall by a broad base, the peritoneum being reflected over the entire remaining surface. The attaching fold of the peritoneum is frequently called the suspensory ligament. The peritoneum, or coelomic epithelium, can be dissected easily from the surface of the liver or the kidney and its extreme thinness and delicacy noted. It consists of a single layer of cells.
Most of the abdominal organs are suspended from the dorsal wall of the body cavity by delicate membraneous sheets, or mesenteries. Similar sheets between the organs are the omenta. The stomach is suspended by a mesogaster, which extends as a free fold along the body as far as the anterior mesenteric and lienogastric arteries. It encloses these, and is attached to the spleen, pancreas, stomach, and anterior end of the intestine.