324 ME. "W. B. S. BENHAM ON THE MUSCULAE 



gives off similar bundles (70, 71) to the next two entochondrites, as well as bundles (74, 

 75, 76, 77) to the fourth, fifth, sixth, and seventh entapophyses. 



It is continued backwards on the floor of the abdomen, after giving off its last slip, 

 and is inserted into the metasomatic sternite. 



No. 4. The Inter-entapophysial Muscles. — Of these there are four (best seen in 

 PI. LXXV. fig. 2) :— 



4 a. A small one running from the hinder edge of the first entapophysis to the 



anterior inner face of the second. 

 4 b. A larger one from the first to the third. 

 4 c. From the first to the fourth. 

 4 d. From the first to the fifth. 

 These lie successively lower, no. 4 a being uppermost. 



No. 78. The Arthrotergal Muscle (PL LXXV. fig. 2).— This large muscle passes from 

 the tergum of the prosoma to the tergum of the mesosoma, across the joint ; it assists 

 in flexing the prosoma on the mesosoma. 



No. 5. Inter sternal or Longitudinal Muscle. — Rising from the dorsal face of the 

 plastron close to the posterior process of this structure, it passes from segment to 

 segment of the mesosoma, being attached in each case to the mesosomatic ento- 

 chondrites, and ending in the metasomatic sternite, being fixed near its anterior edge 

 (PL LXXV. fig. 3). 



The Longitudinal Muscles of the Metasoma. 



No. 6. Internal Pygo-tergal Muscle. — Arising close to the median plane, from the 

 membrane (mb) attached to the dorsal process of the post-anal spine, it passes almost 

 directly forwards, being attached partly to the carapace (6) ; then passing forwards 

 it is attached successively to the inner faces of the metasomatic, the sixth, and the 

 fifth entapophyses, by its branches 91, 92, and 93 respectively. 



No. 7. Middle Pygo-sternal. — Arising also from the membrane above mentioned 

 more laterally than no. 6, it passes laterally forwards, to be inserted into the carapace, 

 splitting into branches 94, 95, which are inserted into that part of the metasomatic 

 sternite (p, ah, st) which rises sharply upwards to join the carapace. 



No. 8. The External Pygo-tergal has the same arrangement as no. 7, but is placed 

 more laterally, and slightly ventrally ; its slips to the metasomatic sternite are lettered 

 96, 97. 



No. 9. Tlie Ventral Entapophysio-pygal. — This muscle arises below no. 6 in the 

 membrane of the main part of the spine, runs forwards, and is inserted into the 

 seventh, sixth, and fifth entapophyses on their outer faces by branches 90, 88, and 89 

 respectively. 



No. 10. The Inner Sterno-pygal arises in membrane at the basal portion of the spine, 



