The Internal Anatomy of Spiders 



to the basal segment of the appendage. There are also muscles 

 within the appendages that produce the movement of the separate 

 segments of the appendages. Figure 151, which represents the 

 musculature of a leg of Thelyphonus, one of the Pedipalpida, 

 will serve as an illustration of the arrangement of the muscles in 

 the leg of an arachnid. 



The muscles of the sucking stomach. — The muscles of the 

 sucking stomach are also very prominent; these are discussed 

 in the section of this chapter treating of the alimentary canal. 

 The muscles of the abdomen. — It is much more difficult 

 to trace out the muscles of the abdomen than it is those of the 

 cephalothorax. In the abdomen the muscular system is greatly 



reduced and other viscera are so greatly 

 developed that the muscles are overshadowed 

 by them. Schimkewitsch ('84) gives a diagram 

 showing the arrangement of the principal 

 muscles of the abdomen of Aranea (Fig. 149). 

 In this figure are represented the three 

 vestiges of the endoskeleton of the sac-like 

 part of the abdomen (Fig. 149, en 

 1, en 2, en 3,); these I have des- 

 ignated as the first, second, and 

 third abdominal endosternites re- 

 spectively. 



The most prominent of the 

 muscles of the abdomen is a series 

 extending from the pedicel of the 

 abdomen to the three endosternites 

 successively and from the third endosternite to the spinnerets. 

 These have been named the longitudinal ventral muscles. 



From the second and third endosternites there extend two 

 pairs, one from each, of dorsoventral muscles. These are the 

 muscles that are attached to the two pairs of more prominent 

 muscle impressions, that appear externally as depressed points 

 in the dorsal wall of the abdomen. 



To the first abdominal endosternite are attached in addition 

 to the longitudinal muscles, muscles from the book-lungs, and 

 a muscle from the opening of the reproductive organs. 



To the second abdominal endosternite are attached several 

 muscles extending to the body-wall. 



Fig. 151. 

 THE MUSCLES OF A LEG 

 OF THELYPHONUS 

 (after Borner) 



144 



