jS Practical Zoology. 



the left of the dorsal fin and on to the head. Remove the skin 

 of this side, carefully leaving the white muscles beneath undis- 

 turbed ; scrape part of the skin clean on the inside ; note the 

 arrangement of the scales as seen on each side of the skin ; look 

 also for traces of the lateral line on the inside of the skin. Hold 

 the skin up and look , through it toward the light, alternately 

 stretching and shortening it, noting especially the lateral line. 

 Roll the skin lengthwise, with the scales outermost, to see how 

 the epidermis passes from one scale to another. 



20. Observe the parallel transverse markings on the muscles 

 along the body. 



2 1 . Cut and scrape away all the muscle of this side of the body 

 down to the bones, and make out the central backbone, with its 

 bony projections above and below. Bend the dorsal and anal fins 

 from side to side, to show the bones which support these fins and 

 the relation of these fin supporters to the projections of the 

 backbone. 



22. Break across the backbone under the center of the second 

 dorsal fin, and remove one piece, or vertebra, of the backbone ; clear 

 away all muscle and other tissue, and make out the following parts : 



a. The central body, or centrum, shaped like an hourglass 

 and hollowed at each end. 



b. Two projections extending upward, soon uniting to form 

 one spine, the neural spine. 



c. The archway formed above the body of the vertebra is the 

 neural arch. 



d. A similar arrangement below, forming the hemal arch and 

 hemal spine. 



Make a drawing of this vertebra as seen from the side ; another 

 as seen from the front. 



23. In like manner remove and study a vertebra from a point 

 opposite the center of the first dorsal fin, with the ribs attached 

 to it. What are the differences between these two vertebrae ? 



24. Thoroughly clean the last vertebra, and study carefully its 

 relations to the caudal fin. 



