Page:The Eurypterida of New York Volume 1.pdf/35

 plate, termed the endocranium, plastron or entostemon, which in its turn forms the fulcrum for other important muscles. Owen has shown that the glabellar furrows, or rather the entapophyses or infoldings to which the furrows correspond, are the bases of the powerful levators of the preabdomen and also of the muscles which serve to steady the entosternon while the latter furnishes the fixed points for the flexors or depressors of the preabdomen and the important muscles that hold and move the coxal joints of the legs. [graphic]

The glabellar furrows of Eurypterus thus correspond quite precisely in position and extension to those of Limulus and the appendages on the ventral side are entirely homologous and of like position and structure; hence it is to be inferred that the same system of muscles existed in Eurypterus as in Limulus, that also Eurypterus may have possessed a cartilaginous entosternon and that the glabellar furrows served as bases for the levators of the preabdomen and the lateral levators of the entosternon. These furrows are also well developed in species of Stylonurus, as.