AND ENDOSKELETAL SYSTEMS OF LIMULUS. 335 



Various plastro-entapophysial muscles are shown attached to the first ent- 

 apophysis. One sees the inter-entapophysial muscles (4) passing from one 

 entapophysis to the other, the tergo-pygals (6, 7, 8) and entapophysio-pygals 

 (91, 92, 93), the external branchials (20), the small veno-pericardiacs (68) 

 passing outwards and upwards across the intersternals. The larger vertical 

 abdominals (12) also pass across the intersternals. Besides these the cut 

 bases of the entapophyses are shown, and connecting these the inter-entapo- 

 physial cartilages (ec) ; and at the sides of the anterior part of the figure are 

 the lateral cornua of the plastron with their muscles 57, 58. 



On the left side of the figure the liver and genital organ have been 

 removed, so as to expose the body of the entosternite or " plastron " (P) and 

 its dorsal process. The dorsal entapophysio-plastral (1) is now seen passing 

 across the vertical muscles, and giving off various slips to the entapophyses. 

 The pygal muscles and the cartilaginous band have been removed. 

 Fig. 2. On the left side the dissection is more superficial than on the right : the course 

 of the dorsal entapophysio-plastral muscle is more completely shown, the 

 inter-entapophysials having been removed. The anterior cornua of the plas- 

 tron (A.c. en), with their muscles (49, 50, 51), are also seen ; and posteriorly 

 the sterno-pygals (10, 11) and entapophysio-pygals (88, 89, 90). The abdo- 

 minal sternites (sW) lying on the floor of the mesosoma are also exposed. 



On the right side of the figure the above-named muscles have been removed, 

 so as to show the course of the ventral entapophysio-plastral muscles (2& 73) 

 with their slips to the entapophyses. The entapophysio-metaplastrals have 

 been cut, so as to show the posterior median process of the plastron (pcen). 



PLATE LXX1V. 



Fig. 1. All the overlying muscles have been removed, and thus the floor of the animal 

 is exposed. On the right the distribution of the ventral longitudinal (3) 

 and the intersternal muscles (5) is seen. The slips passing from the various 

 sternites to the entapophyses, and the vertical muscles (12) inserted in the 

 abdominal sternites are also seen. 



On the left the aforenamed muscles have been removed in order to show 

 the venous-collecting sinus (Vc) lying at the side of the floor of the animal, 

 passing anteriorly above the plastron, where it has been cut. The veno- 

 pericardiac muscles (68) are shown springing from this canal, and are turned 

 towards the middle line. Passing up at the side of the canal are shown the 

 hollow tendons of the branchio-thoracic muscles (18), each ending anteriorly 

 in a muscular portion, which has been cut. Attached to the side of each 

 abdominal entochondrite is seen a small muscle (48), the internal branchial. 

 vol. xi. — part x. No. 4. — May, 1885. 3 e 



