8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 10/ 



region of the cranium on which arise the muscles of the maxillae 

 and the mandibles (fig. i B, mdmcl) from that on which the facial 

 muscles take their origin. The facial muscles comprise two distinct 

 groups : an upper group, including the extrinsic muscles of the labrum 

 (Ibrmcls), except in adult Diptera, the precerebral dilators of the 

 pharynx (phmcls), and the dorsal hypopharyngeal muscles (hphmcl), 

 or "retractors of the mouth angles" ; and a lower group of intraclypeal 

 muscles, which are the dilators of the cibarium (cbmcls). The 

 cibarial muscles are always separated from the hypopharyngeal and 

 pharyngeal muscles by the frontal ganglion (FrGng) and its brain 

 connectives. 



In recent years it has become the custom, following Crampton 

 (1932) and Snodgrass (1935), to give the name "postfrontal sutures" 

 to arms of the cleavage line that diverge to points usually between 

 the eyes and the antennae (fig. i D), while the term "frontal sutures" 

 is restricted to the arms in positions mesad of the antennal bases (F). 

 In either case, however, the divergent arms of the "epicranial suture" 

 on the head of an immature insect are the preformed lines of the 

 future exuvial splits that branch from the end of the coronal cleft. 

 As DuPorte (1946) has shown, the two supposed "sutures" are the 

 same thing in different positions. 



The idea that the arms of the cleavage line on the head are two 

 different "sutures" according as they go laterad of the antennae or 

 between them has led to some curious interpretations of the insect 

 head structure. Ferris (1942), for example, calls the lines in the first 

 case the "postfrontal sutures," and connects them with the temporal 

 sulci that in some insects run back over the top of the head mesad of 

 the compound eyes and then downward on the posterior surface to 

 the bases of the mandibles. The continuous line thus established he 

 calls the "great suture" of the cranium, which he asserts is the line of 

 union between the oculoantennal segment and the mandibular segment 

 of the head, the tritocerebral segment being assumed to have been 

 obliterated. The mantis is cited as an example demonstrating this 

 alleged continuity in the parts of the "great suture," and, in fact, on 

 the head of an adult mantis (fig. 4D) the arms of the cleavage line 

 (CL) do appear to turn back and become continuous with the tem- 

 poral sulci (ts). The continuity, however, is not present in the 

 nymph, and even in the adult the external appearance is misleading. 



An examination of the inner surface of the adult mantid cranium 

 (fig. 4G) shows that the facial area is fortified by a complex of 

 ridges braced laterally against the circumocular ridges (OcR) and 

 continued dorsally into the temporal ridges (TR). From the lower 



