CHAPTER VIII 

 THE MUSCULAR AND SKELETAL SYSTEMS 



1. The Muscular and Skeletal Structures of the Tail. 



Cut a cross-section through the tail just anterior to the 

 cut made for the injection of the arteries. Shave away a 

 section until the end of a vertebra is reached at which point 

 four rays, white areas of calcification which form a cross, 

 will be seen. Examine, using a hand lens. 



The outer layer is the integument bearing the placoid 

 scales. Next is a series of voluntary muscles made up of 

 myotomes or muscle segments which appear as whorls in 

 the section. The layers are separated from each other by 

 myosepta or myooommae composed of connective tissue. 

 The myotomes are separated by an horizontal skeletogen- 

 ous septum into a dorsal portion, the epaxial muscles, 

 and a ventral portion, the h3rpaxial muscles. The muscles 

 will not be further studied in the skate; in general they 

 show segmentation. 



The vertebra shows these structures : a concave centrum 

 with a dorsal neural arch forming the neural canal for the 

 spinal cord and a ventral haemal arch for the caudal ar- 

 tery. The arch ends in a haemal spine corresponding to 

 the neural spine of the neural arch. Continuous with each 

 is a skeletogenous septum running to the median dorsal 

 and ventral lines. 



Drawing 26. Draw the cross-section of the tail. 



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