THE RELATIONSHIP OF THE CHELICERATE ARTERIAL SYSTEM ...

FIRSTMAN-CHELICERATE ARTERIAL SYSTEM AND ENDOSTERNITE 23each other at their posterior ends by a bridge which extends horizontally posteriad to thesecond abdominal segment. The endosternite receives the insertions of four pairs ofdorsal suspensors, three pairs of ventral suspensors, and two pairs of transverse suspensors.The positions of the anterior and posterior transverse suspensors are marked respectivelyby anterior and middle bridges which join the right and left sides of the endosternite(Fig.16). The space enclosed by these two bridges forms the anterior fenestra, andbehind the middle bridge there is a smaller posterior fenestra which separates it from theposterior bridge. The right and left extremities of the anterior transverse suspensor originatefrom the lateral margins of the cephalothorax, but the posterior transverse suspensoris deflected dorsomedially so äs to become anatomically and functionally indistinguishablefrom the posteriormost pair of dorsal suspensors (Fig. 16A). A close examinationof the transverse suspensors shows that the connective tissue fibers which strengthenthem run across the respective bridges; hence, the anterior and middle bridges may beinterpreted äs morphological components of (äs derived from) the transverse muscles.Order Schizomida-Except for their small size, schizomids are vety similar to thelyphonids,externally and internally. Millot (1942a) split the heterogeneous order Pedipalpi,and put schizomids, thelyphonids and amblypygids into respective Orders of theirown. Later, however, Millot (1949c) and Kaestner (1968) reunited the schizomids andthelyphonids äs families of the order Uropygida. Nothwithstanding this, there is a currenttrend to separate schizomids and thelyphonids (Petrunkevitch, 1955;Savory, 1964),and to recognize both äs separate Orders.right chelicera propeltidium left dorsal suspensor muscles of the endosterniteanterior bridge of the endosterniteposterior bridgeof the endosterniteFig. 17.-A: midsagittal view of the cephalothoracic region of Trithyreus pentapeltis (orderSchizomida), showing a superimposed lateral view of the left side of the endosternite; B: dorsal viewof the endosternite.