336 JIE. W. B. S. BENHAil ON THE MTTSCCLAR 



Outside the canal are seen the various branchial muscles rising from the 

 mesosomatic appendages to their attachment in that portion of the entapo- 

 physial ligament (ec) which partly embraces each entapophysis. 



Fig. 2. A portion of the venous-collecting sinus, removed and enlarged ; in front the 

 wall has been cut to show the apertures (O) of the descending vessels to the 

 mesosomatic appendages. The hollow portions of some of the branchio- 

 thoracic muscles (18) are seen uniting to form the large muscular portion. 

 Some of the branchial muscles are also seen. 



Fig. 3. Two mesosomatic appendages seen from below. 



VIII. The deep face of the anterior plate of the eighth appendage. The 

 appendage is turned forwards. The posterior plate — except the portions 

 which bear the gill-lamellse (/), and the " stigmata " (sfg) leading into the 

 hollow tendons of the branchio-thoracic muscles — has been dissected away. 



IX. is the inner face of the posterior plate of the ninth appendage, after 

 removal of the anterior face. At the base of each appendage is an abdo- 

 minal sternite (s) with muscles passing in various directions from it. The 

 second pair of entapophyses (cut. 2) are seen with a portion of the entapo- 

 physial ligament (ec), to which some of the branchial muscles (21, 22, 23) 

 are attached. Various sclerites (a.p.c) with their muscles (23, 48, 112, 113, 

 114, 115) are also seen, which lie on the surflice of the appendages. The 

 tendons (ts) of the branchio-thoracic muscle are shown. 



Fig. 4. Inner surface of posterior plate of the seventh appendage, " genital operculum." 

 The genital duct (gd) cut short is seen. 



Fig. 5. Inner surface of anterior plate of the genital operculum. The stigmata (sfg) 

 of the basal portion (ts) of the branchio-thoracic muscle. The genital duct 

 and aperture (ffp), and the first pair of entapophyses are shown. 



PLATE LXXV. 



Longitudinal sections. 



Fig. 1. Shows two entocoxitcs (Enc.r) with their muscles (25): the camerostome and 

 basal part of first appendage and its muscle (24) : the entosternite or 

 plastron (P) and its muscles (49, 50, 51, 52, 53) : the course of the branchio- 

 thoracic muscle (18) with its hollow tendons (ts) and their apertures (stg): 

 the pygal muscles, attached partly to the tergum of the metasoma and partly 

 to the hinder entapophyses (6, 7, 90, 91, 92). A few only of the branchial 

 muscles (20, 22, 23) and two of the vertical mesosomatic muscles (12) are 

 represented. This figure also shows the claw-like termination of the second 

 appendage (ii) characteristic of the male Limuliis iwlyphemus. The other 

 prosomatic appendages have been cut short. 



