460 



ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 31 



simply the result of the secondary division of the cranial wall by 

 the linear inflections, or " sutures," forming the internal ridges. 



Above the line of the subgenal and epistomal sutures there are 

 five principal head areas (fig. 8). On the face between the frontal 

 sutures is the median, triangular frons {Fr). The side walls of the 

 head between the frontal and occipital sutures, separated above by 

 the coronal suture, are the parietals {Prtl), inclosing the compound 

 eyes and the antennal sockets. The top of the two parietals is 

 known as the vertex, and the parts below the eyes are the genae. 

 On the back of the head, between the occipital and postoccipital su- 

 tures, is the occiput, or 

 occipital arch (Oc). 

 The dorsal part of the 

 arch is usually termed 

 the occiput in a more re- 

 stricted sense (fig. 9 B, 

 Oc), and the lateral 

 parts the postgenae 

 {Pge). In the grass- 

 hopper Melanoplus a 

 suture on each side sep- 

 arates the dorsal occipi- 

 tal area from the lateral 

 postgenal areas. The 

 posterior rim of the cra- 

 nium behind the post- 

 occipital suture is the 

 postocclput (fig.8,F6>c). 

 The postocciput bears 

 the occipital condyles 

 (occ) by which the an- 

 terior neck plates artic- 

 ulate with the head (fig. 12 A, cvpl). In most insects the postocciput 

 is a narrow sclerotic flange to which the neck membrane is attached 

 (fig. 9 B, Poc) ; but it is often much reduced, except for remnants 

 bearing the occipital condyles (fig. 13), and it is sometimes com- 

 pletely obliterated. 



Below the line of the subgenal and epistomal sutures (fig. 8, sgs, 

 es) there is on each side of the head a narrow marginal band above 

 the bases of the mouth parts (fig. 12 A), and on the front of the 

 head a broad area, known as the clypeus (figs. 8, 12 A, Glp), which 

 supports the labrum (Lm). Just as the parts of the subgenal su- 

 ture lying before and behind the posterior mandibular articulation 

 (fig. 8, a') are distinguished for descriptive purposes as the pleuro- 

 stomal suture (ps) and the hypostomal suture (hs), so the corre- 



FiGUBB 10. — Facial viow of the head of a roach, 

 Blatta orientalis 



Aclp, anteclypeus ; Ant, antenna ; as, antennal suture ; 

 at, anterior tentorial pit ; cs, coronal suture ; E, 

 compound eye ; Fr, frons ; fs, frontal suture ; Oe, 

 gena ; LbPlp, labial palpus ; Lm, labrum ; Md, man- 

 dible ; Mx, maxilla ; MxPlp, maxillary palpus ; Pclp, 

 postclypeus ; sas, substantennal suture ; sys, subgenal 

 suture. 



