OJs THE MUSCULAR AND EXDOSKELETAL SYSTEMS OF SCOKPIO. 



Part III. Description of the Muscular and EndosJceletal Systems of Scorpio. 



By Miss E. J. Beck. 



For this work, in which I have been assisted by the kind supervision of Professor 

 Lankester, I have used the Ceylon Scorpion {Buthus cyaneus) for dissecting, whilst 1 

 have also referred to a series of sections of the small Scorpion {Scorpio italicus), by 

 means of which I have been able to find some small muscles which I should have 

 otherwise passed unnoticed, and some which are too small to be seen by the naked 

 eye. 



I have named the muscles as much as possible from the names of the two points to 

 which they are attached. Thus in many cases the names are long and awkward. In 

 order to somewhat modify this difficulty I have given to each muscle a separate number, 

 and have numbered them similarly in the figures. 



It must be remembered that each of the muscles which I shall mention is repeated 

 in a corresponding position on the opposite side of the animal, with the exception of 

 a few which are situated in the median line, and which I shall particularly point out. 



Before giving a description of the muscles of the Scorpion it will be necessary to 

 examine the general form of the animal, and more particularly its skeleton, external 

 and interna], with any other parts that form attachments for muscles. 



External Skeleton. — The body of the Scorpion may be divided into three parts, the 

 prosoma, mesosoma, and metasoma, each of which represents six segments, and corre- 

 sponds precisely to the similarly named part in the King Crab. The segments are 

 indicated partly by sclerites and partly by appendages. Following the metasoma is the 

 postanal spine or sting. 



Dorsal Sclerites. — The whole of the dorsal surface of the prosoma is covered by one 

 large chitinous plate, the cephalothoracic plate or carapace [car). This is followed by 

 seven wide sclerites, six of which represent the six segments of the mesosoma (vn-xii), 

 whilst the seventh (xiii) belongs to the first segment of the metasoma, and is fused 

 towards its posterior end to a corresponding sclerite on the sternal surface. Posteriorly 

 this sclerite becomes narrower, and is followed by five narrow cylindrical sclerites 

 (xiv-xviii), which are formed by the fusion of the tergite of the dorsal surface with the 

 sternite of the ventral. 



Apjjcndages and Sternal Sclerites. — On the ventral surface of the prosoma there are 

 six leg-like appendages, which indicates that six segments have coalesced to form the 

 carapace. 



The first appendage, chelicera (i), is small, consisting of three sclerites : the proto- 

 merite or coxa, the deutomerite, and the tritomerite. The deutomerite is drawn out, 

 and forms with the tritomerite a pincer. This pair of appendages is situated in front 

 of the mouth and projects anteriorly. 



