NO. lO KKKDING ORGANS OF AKACI I NinA^SNOOCRASS 37 



tically ail apodemal structure. The cheloiicthid epistome is termed 

 by Chamberlin the "intermaxillary jugum" hccause its distal part is 

 united with tlie pedipalp coxae, which are c(»mm(jnly called "maxillae" ; 

 l)ut on its under surface are attached the usual dorsal muscles of the 

 ingestion apparatus (F), showing that the plate in question is that 

 here termed the ei)istome in other arachnids. The epistome is similarly 

 iiivaginated or overgrown in the Ricinulei and some Acarina, and in 

 the last order is known as the "subcheliceral plate." 



The under surface of the lahrum is continued posteriorly as the 

 dorsal wall of the preoral food passage, and is produced into an elon- 

 gate lobe (fig. 12 B, tpfj) enclosed between the mesal surfaces of the 

 pedipalp coxae (which latter, as shown at 15, are spread apart). The 

 under surface of the lobe is deeply channeled lengthwise, and receives 

 the narrow under lip (Ipg), which carries a high, crestlike ridge on 

 its upper surface, as seen in cross section at D. Chamberlin (1931) 

 likens these two structures to a pair of jaws lying one above the other. 

 The upper grooved "jaw" he terms the taplirocjnatJi, the lower crested 

 "jaw" the lophoguath. 



The so-called lophognath, or under lip. is a laterally compressed, 

 tapering, median lobe projecting forward from the venter of the 

 prosoma between the bases of the pedipalp coxae (fig. 12 B, Ipg), 

 and would thus appear to be a sternal structure, as said by Pocock 

 (1902). Chamberlin shows that the lophognath is attached by two 

 basal arms to the pedipalp coxae, but its form and structure do not 

 suggest that the lophognath itself is of coxal origin. 



The relation of the taphrognath and the lophognath to each other 

 is shown diagrammatically at F of figure 12, in which the lophognath 

 {Ipg) is partly exposed by being pulled down from the groove of the 

 taphrognath (tpg). The opposing surfaces of the taphrognath and 

 the lophognath are shown by Chamberlin to be corrugated by nu- 

 merous fine, closely set, transverse ridges, fringed with minute spines 

 directed inward. The exposed lateral surfaces of the two lobes are 

 also ridged, but on these areas the ridges are somewhat farther apart. 

 On the crest of the taphrognath are inserted the fibers of a large flat 

 muscle (C, F, did) having its origin on the under surface of the 

 invaginated epistome (Epst). 



At their inner ends the taphrognath and the lophognath are united 

 by a union of the lips of the former with the sides of the latter (fig. 

 12 F). There is thus formed here the true oral aperture, which opens 

 immediately into a relatively small, j)ear-shai>ed pharyngeal sack 

 (Phy). This organ shows in cross section (E) the usual structure of 

 the arachnid pharynx ; the concave dorsal, ventral, and lateral walls 



