10 GUIDES FOR VERTEBRATE DISSECTION 



pelvic girdle and bears a few radialia on its posterior surface. 

 The basale metapterygii extends directly posterior and bears a 

 larger number of radialia on its lateral surface. In the skeleton 

 of the pelvic fin of the male note that the posterior radial is 

 enlarged and extends directly posteriorly into the clasper in 

 such a way that it appears as a direct continuation of the basale 

 metapterygii. 



Sketch the skeleton of the fin, natural size, bringing out all 

 of these points. 



In the skeleton of the anterior dorsal fin make out a large 

 basal plate (basale) bearing in front the strong spine of the fin 

 and behind a few (how many?) polygonal radialia, beyond which 

 are actinotrichia as in the paired fins. Compare the second dorsal 

 with the first. Is there any basal skeleton in front of the spine? 

 To which category basalia or radialia does the spine belong? 



Sketch the skeleton of both dorsal fins, natural size. 



INTERNAL STRUCTURE 



Lay the fish on its back on the dissecting-board and, beginning 

 just in front of the pelvic fins, make an incision about a quarter 

 of an inch to one side of the median line. Carry the cut forward 

 until you reach the skeletal arch (pectoral girdle) between the 

 pectoral fins. Be careful not to cut anything except the body 

 wall, especially in front. (Most of the material supplied by 

 dealers has this cut when sent out.) 



This lays open the body cavity or coBlom (better, metacoele), 

 lined with a smooth membrane, the peritoneum. Notice that the 

 peritoneum covers not only the outer wall of the body cavity 

 but extends over all the enclosed viscera. 



Pull apart the body walls and, without disturbing anything, 

 make out the chief viscera as follows: Anteriorly a large liver 

 with two main lobes. Which lobe bears a smaller lobule? Dorsal 

 to the liver and extending a little beyond it on the left side is 

 the stomach which bends on itself posteriorly like the letter J. 

 The bend divides it into an anterior (left) cardiac and a posterior 

 pyloric portion. 



At the bend of the J is a large triangular spleen. At the end 

 of the pylorus the short duodenal portion of the intestine begins. 

 This is succeeded almost immediately by the large intestine, 



