AND ENDOSKELETAL SYSTEMS OF LIMULUS. 325 
and runs slightly outwards and forwards to the uprising portion of the post-abdominal 
sternite, to which it is attached. Itis more laterally placed than no. 9, and below no. 7. 
No. 11. The Outer Sterno-pygal arises from the basal membrane of the spine more 
laterally than no. 10. Passing below no. 8 it is attached to the floor of the metasoma. 
No. 61. A few muscular fibres, rising in the floor of the fourth mesosomatic segment, 
run to the fifth and thence to the sixth segment, and end in the metasomatic sternite, 
a good deal mixed with nos. 3 and 5. 
Il. Dorso-ventral Muscles. (Plate LXXV.) 
No. 12. The Vertical Mesosomatic Muscles—Of these there are six on each side. 
Each is inserted into one of the six mesosomatic (or abdominal) entochondrites on its 
outer edge, and rising slightly obliquely across the bundles of no. 1, between the 
branches of which it passes, is attached to the tergum anteriorly to the base of each of 
the entapophyses, its general course being vertical. [It is especially noteworthy that 
the first pair of this series passes from the entochondrite of the genital operculum to 
the prosomatic tergum, being attached just in front of the great entapophysis on each 
side.—E. R. L.] 
No. 13. The Oblique Entapophysio-sternals—A muscle from the second mesosomatic 
entochondrite passes backwards, upwards, and outwards above no. 3, and below the 
branches of no. 2, to its attachment to the deep (free) end of the fourth entapophysis. 
No, 14. A muscle, with a similar course, from the third mesosomatic entochondrite 
to the fifth entapophysis. 
No. 15. A similar muscle from the fourth mesosomatic entochondrite to the sixth 
entapophysis. 
No. 16. A similar muscle from the fourth mesosomatic entochondrite to the metaso- 
matic (seventh) entapophysis. 
No. 17. A similar muscle from the fifth abdominal entochondrite to the metasomatic 
(seventh) entapophysis. 
No. 18. The Branchio-thoracic Muscles.—A series of muscles pass from the hollow 
tendons which open at the stigmata of the mesosomatic appendages. ‘There are six 
pairs of these. Each tendon has attached to it a thickening bundle of muscle which 
in its passage upwards and forwards passes outside no. 12 muscle to the inside of the 
entapophyses, beneath the dorsal lateral plastro-tergal muscle (52) to its attachment 
to the carapace in the prosoma, alongside that of the coxo-tergal muscles, but nearer 
the median plane. 
No. 19. From the bundle attached to the last stigma (see Pl. LXXV. fig. 1), before 
it has joined those arising from the anterior stigmata, there rises a muscle which 
passes more directly upwards than the mass of the branchio-thoracic, and is attached 
to the inner posterior face of the second entapophysis. 
