AND ENDOSKELETAL SYSTEMS OF LIMULUS. 329 



IV. Muscles connected with the Plastron or Prosomatic Entochondrite not described 



in the preceding Sections. 



No. 49. The Tergo-proplastral Muscles (Anterior Plastro-tergals). — This muscle (r&ndl) 

 is inserted into the inner side of the anterior cornu of the plastron, and passes out- 

 wards, upwards, and forwards to its attachment to the carapace, slightly in front of and 

 mediad of the muscle 25. 



No. 50. A smaller muscle, inserted behind 49, passes slightly forwards and upwards, 

 in front of 24, to its attachment to the prosomatic carapace. 



No. 51. Similarly inserted, passing behind 24 to its attachment to the carapace, 

 behind and mediad of the third coxotergal (25 b). 



No. 52. The Borso-lateral Plastro-tergal. — This (r and I) is inserted into the dorsal 

 process of the entochondrite, passes backwards, upwards, and outwards across no. 18, 

 and is attached to the carapace in the same line with this latter muscle. 



No. 53. The Borso-lateral Entapophysio-plastral. — This muscle (r and I) is inserted 

 on the hinder edge, near the base, of the dorsal process of the plastron, and passes 

 upwards and backwards, and only very slightly outwards, crossing the attachments of 

 no. 2, to the first entapophysis, to the anterior inner edge of which it is attached. 



No. 54. The Anterior Entapophysio-mesoplastral Muscles. — Each of these (r and I) 

 rises along the middle line of the dorsal surface of the " body " of the plastron, and 

 passing across the attachment of no. 2, outwards, and slightly backwards and upwards, 

 is attached to the first entapophysis alongside 53. 



No. 55. The Posterior Entapophysio-mesoplastral Muscles. — Each (r and /) rises from 

 the base of the posterior process of the plastron, and passing outwards, across no. 2, 

 goes to the first entapophysis, to which it is attached close to 54. 



No. 56. The Posterior Entapophysio-metaplastral Muscles. — Each (r and I) rises 

 below 55, from the side of the posterior process, and passing outwards and backwards 

 crosses no. 2, and is attached to the second entapophysis. 



No. 57. The Lateral Tergo-proplastral Muscles. — A short muscle (r and /) is inserted 

 into the distal end of the anterior lateral cornu of the plastron, and is attached to the 

 carapace between nos. 25 (b and c), but outside the line formed by these muscles. 



No. 58. A similar muscle (r and I) is inserted into the posterior lateral cornu, and is 

 attached behind 57, between 25, c and d. 



No. 59. A small muscle is inserted a short way down the posterior lateral cornu, and 

 is attached to the carapace close to 25 (d). 



No. 72. The Vertical Entapophysio-metaplastral Muscles. — Each (r and I) rises 

 below 56, from the edge of the posterior process of the plastron, and passes to the third 

 entapophysis. 



No. 67. Plastro-buccal Muscle. — From the under-surface of the entochondrite, a few 

 muscular fibres go to the oesophagus close to the mouth. 



3d2 



