NO. 3 



INSECT IIEAI 



-SNODGRASS 



49 



muscles of the gnathal appendages, especially those of the mandibles, 

 show a highly specialized condition in that they are mostly separated 

 from their sternal connections and united upon a common transverse 



,-DT 



Fig. 21. — The hypopharyngeal apophyses and the tentorium. 



A, under surface of head of Lithobius, mandibles and maxillae removed, 

 showing suspensorial plates (HS) of hypopharynx suspended from points (d) 

 on margins of head, and hypopharyngeal apophyses (HA) invaginated from 

 their inner ends and connected by ligamentous bridge (/) beneath pharynx. 



B, Head of Scolopcndra, ventral, maxillae and right half of cranium re- 

 moved, showing attachment of mandibular adductors (KL, KL) on ligament 

 uniting the hypopharyngeal apodemes. 



C, Sciitigera forceps, ventral view of hypopharynx {Hphy), suspensorial 

 plates (HS), their apodemes (HA) and vmiting ligament (/). 



D, Heterojapyx gaUardi, ventral view of right maxilla, hypopharynx (Hphy), 

 and hypopharyngeal apodemes (HA) upon which arise muscles of the maxilla 

 (admx), the labium (Ibmcl), and the mandibles (not shown). 



E, Ncsoniachilis maoriciis, posterior view of unconnected anterior and pos- 

 terior arms of tentorium (HA, PT), part of the head wall with clypeus (CIp) 

 and labrum (Lin), base of maxilla (Mx), and mandible (Md). 



F, Ephemerid nymph, ventral view of tentorium and part of left side of head, 

 showing anterior tentorial arms (AT) arising from ventral margin of gena 

 (Ge). 



ligament. In the pterygote insects the hypopharyngeal muscles, the 

 ventral dilators of the pharynx, and most of the fibers of the ventral 

 adductors of the mouth part appendages arise on the endoskeletal 

 structure of the head known as the tentoriion. Evidentlv, then, the 



