66 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 8l 



The movable terminal lobe of the chilopod mandible (fig. 26 B, 

 C, Lc) is provided with the same muscles as is the corresponding lobe 

 of the diplopod mandible (A. Lc) and the lacinia of the insect maxilla 

 (figs. 25 C, 30 15, Lc) . The muscle from the lobe to the basal plate in 

 the chilopod jaw is very large (fig. 26 B, C, flcs), suggesting that of 

 Japyx (fig. 30 B. -flcs), and is composed of two groups of fibers. The 

 cranial muscle {ficc) arises by a broad base on the dorsal wall of the 

 head, and is inserted on a slender apodeme from the inner angle of the 

 lobe. In the chilopod mandible, therefore, there is a basal plate (fig. 

 26 B, BP) corresponding with the cardo and stipes of the insect 

 maxilla, but not divided as in the diplopods, and a free terminal lobe 

 {Lc) which represents the lacinia. In retaining the connection of the 

 adductor muscles with the hypopharyngeal apodemes, the chilopod 

 mandible preserves the primitive condition shown by the maxilla of 

 Japyx {fig. 2>o^). 



In the Crustacea and Hexapoda, the mandible, or the jaw part of 

 the mandibular appendage, which may bear a palpus, consists of a 

 single piece. Whatever may be the primitive elements that have 

 entered into its composition, these elements are fused into a solid 

 gnathal organ. There are, hence, never muscles entirely within ^the 

 mandible, except those that pertain to the palpus, when a palpus is 

 present. The mandibular musculature consists exclusively of the 

 muscles that move the appendage as a whole, and these musdles cor- 

 respond with the muscles of the basal plate of the myriapod mandible, 

 or with those of the cardo and stipes of the insect maxilla. 



In the phyllopod crustacean Apits, the large mandibles (fig. 27 A, 

 Md) hang vertically from the wall of the mandibular segment (IV). 

 Each is a strongly convex, elongate oval structure, attached to the 

 lateral membranous wall of the head by most of its inner margins, 

 leaving only a ventral masticatory part projecting below as a free lobe. 

 A single, dorsal point of suspension (a) allows the base of the man- 

 dible to turn on its vertical axis, or to swing inward and outward as 

 far as the membranous lateral head wall will permit. The musculature 

 is correspondingly simple: two dorsal muscles from the tergum of 

 the mandibular segment (IV) are inserted on the! base of the jaw, one 

 (/) on the anterior margin, the other (/) on the posterior margin ; 

 the hollow of the mandible is filled with a great mass of fibers (KL) 

 which converge upon a median transverse ligament (k) that receives 

 likewise the muscles from the opposite jaw. Here, then, is a ventral 

 dumb-bell adductor, as in the diplopods, and two dorsal muscles, which 

 may function either as productors and reductors, or as anterior and 

 posterior rotators. It is not clear as to what constitutes the mechanism 



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