A^D EXDOSKELETAL SYSTEMS OP LIMULUS. 337 



Fig. 2. Shows the relation of the pericardium [Pc) and the venous collecting sinus {vc) 

 to the other parts and to one another. To be especially noticed are the 

 pericardio-ventral or veno-pericardiac muscles (OS) : the vertical mesosomatic 

 muscles (12): the ventral pygal muscles (9, 10, 11): the muscular stomach 

 (s) vrith its muscle (66) to the subfrontal area {sfa). Also the intertergal 

 muscle (78) flexing the abdominal upon the thoracic region. 



Fig. 3. Shows the plastro-tergal muscles (19 to 54) : the genital duct in appendage vii : 

 the inter-entapophysial muscles (4) : the course of the ventral longitudinal (3) 

 and intersternal muscles (5), with their various slips to the entapophyscs. 

 Also the vertical abdominals (12). 



Fig. 4. External view of two entapophyses of the left side (twice nat. size) showing the 

 cartilaginous interentapophysial ligament {ec) swelling out to partly embrace 

 the entapophysis, and serving for the attachment of various muscles which 

 pass to the mesosomatic appendages. The area of attachment of two of the 

 external branchial muscles (20) is shown. 



Fig. 5. Internal view (mediad face) of two entapophyses of the right side (twice nat. 

 size). The cartilaginous interentapophysial ligament is seen, and various 

 muscles attached to the entapophysis itself. Also the area of attachment 

 of two of the vertical mesosomatic muscles (12) is seen on the tergite. 



Fig. 6. A three-quarter view from in front and within of an entapophysis and cartilage. 



Fig. 7. A three-quarter view from behind and without, showing the cut end {ect) of 

 that part of the inter-entapophysial ligament that passes from one swelling to 

 another. The swelling of the ligament is deeply cupped and fixed to the 

 chitinous entapophysis. It contains a core of capsuligenous tissue, whilst 

 the rest of the ligament consists of fibro-massive tissue. 



PLATE LXXVI. 



Fig. 1. Inner face of the prosomatic and mesosomatic carapaces, showing the areas of 

 attachment of the various tergal muscles. [Unfortunately this figure is very 

 inaccurate and incomplete in respect of the areas of muscular attachment, 

 and must not be relied upon in that matter. — E. R. L.] On the right ludf 

 the areas are left uncoloured, and are more plainly limited than on the left 

 half. The entapophyses are shown, and the ridge (?•/) on each side, corre- 

 sponding to a depression on the exterior. The lateral parts of the terga have 

 a chitinous network j-aised upon their inner surface. In the mesosomatic 

 portion is shown a part (x) of the sternal region which rises to meet the 

 tergite. 



Yx". 2. Shows the relative positions of the entocoxite (whose knobs (Z), to which the 

 tergo-coxals are attached, are seen), the prosomatic entochondrite (phistron) 

 (P), and the mesosomatic entochondrites (s). The hollow tendons {ts) of the 



3e 2 



