The Dissection Of The Dogfish

A Guide for the Dissection of the Dogfish is a book by Lawrence Edmonds Griffin. It covers the examination and dissection of the spiny dogfish, a small shark that abounds along the coasts of the United States.

Excerpt from A Guide for the Dissection of the Dogfish (Squalus Acanthias) The spindle-shaped body tapers from near the middle toward both head and tail; the head is flattened on both the dorsal and ventral sides, while the remainder of the body is nearly round, with a lateral compression which is not pronounced except in the caudal portion. The general color of the back and sides is gray; darkest above, where the skin is spotted with scattered, small, round, light spots. The color of the upper parts shades into the yellow white of the ventral surface. Can head, trunk, and tail regions be distinguished? If so, what characters determine the extent of each? A little above the middle of the side of the body is the lateral line, (distinguished partly by color, partly by being slightly elevated), which extends from the back of the head to the tail. Cut through the skin across the lateral line at several points along the body and notice the canal which lies in the dermis under the lateral line. This is the lateral line canal, which opens to the surface by numerous pores (too minute to be seen), and contains a series of special sense organs along its dorsal and inner surfaces. Near the base of the caudal fin the lateral line canal passes into a groove which continues the lateral line to within a short distance of the edge of the fin. The lateral line canal in its development begins as a groove along the side of the body which becomes closed by the fusion of its edge except in this terminal portion. The open groove does not appear in Eugaleus. In the midline of the body are two triangular dorsal fins, each attached to the body for about half its length. The basal portion of each is thick and muscular, and contains supporting cartilages embedded in the muscles. The remainder of the fin is flexible and semi-transparent, horny finrays being faintly visible between the layers of skin. In front of each fin is a strong spine which seems to serve both as a cutwater and a weapon of defense. (Eugaleus has no spines.) The broad, paired, pectoral fins, having the general characteristics of the dorsals, spring from the ventral edges of the body just back of the head. A hard bar of cartilage connecting the bases of the pectoral fins can be felt through the skin of the ventral surface of the body. This is the ventral part of the pectoral girdle. Farther back, and also on the ventral surface, are the paired pelvic fins. The pelvic girdle can be felt through the skin between the bases of these fins. If the specimen is a male, it will have a fingerlike process projecting backward from the base and along the inner side of each pelvic fin. These organs, which attain a considerable size in adults, are modified portions of the pelvic fin used as copulatory organs. They are named variously claspers, myxopterygia, or pterygopodia. A groove runs along the dorsal side of the clasper from the tip to near the base, where it opens into a long sac (glandula pterygopodia) extending some distance in front of the pelvic fins just within the skin of the ventral surface. By feeling a cartilaginous axis of the clasper can be discovered, which extends to the tip of the organ. On the dorsal surface and near the end of the clasper is a sharp grooved spine on the outer side, and a strongly recurved hook on the inner side, both almost hidden by a flap projecting from the inner edge of the groove. This flap is stiffened by a series of small cartilages similar to the radial cartilages in the bases of the fins. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com

This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1922 edition. Excerpt: ... 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. The spleen is connected with the stomach by the gastro-splenic omentum, formed by an extension of the peritoneal coat of the stomach around the spleen. The liver is connected to the loop of the stomach by the gastro-hepatic omentum in which are the hepatic duct, portal vein, and hepatic artery. Near the stomach it is joined by a fold of the peritoneum from the duodenum, the duodeno-hepatic omentum, which also unites with the mesogaster. The rectum and rectal gland are supported by a second median mesentary, the mesorectum. In Eugaleus the mesentery extends the entire length of the abdominal cavity. It forms a broad sheet attached to the anterior end of the proximal limb of the stomach (mesogaster), to the anterior end of the intestine (mesentery proper), and to the rectum (mesorectum). There is not the reduction of the mesentery which there is in Squalus. The gonads are suspended from the lateral faces of the mesentery above the stomach and intestine. The gastrohepatic omentum forms a broad sheet between the limbs of the stomach, joining the...

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