348 THE ANATOMY OF INVERTEBRATED ANIMALS. 



plate, confluent with the epicranium above and supporting the 

 submentum anteriorly. I think it is probable that these cer- 

 vical sclerites represent the hindermost of the cephalic somites, 

 while the band with which the maxillae are united, and the 

 gensd, are all that is left of the sides and roof of the first max- 

 illarv and the mandibular somites ; the epicranial expansions 

 being mainly formed by the upward and backward extension 

 of the ophthalmic and antennary sterna, which arise out of 

 the procephalic lobes of the embryo. In addition to these 

 externally-visible sclerites, there is a sort of internal skeleton 

 (endocraniwn or tentoriuin)^ which extends as a cruciform 

 partition from the inner face of the lateral walls of the cra- 

 nium, close to the articulation of the mandible, to the sides of 

 the occipital foramen. The centre of the cross is perforated 

 by a rounded aperture, through which the oesophageal nerve- 

 commissures pass. The commencement of the oesophagus 

 traverses the interspace between the anterior processes of the 

 cross ; the tendons of the great adductors of the mandible 

 pass through the lateral apertures ; and the backward contin- 

 uation of the gullet enters the thorax through the posterior 

 aperture, included between the tentorium and the margins of 

 the occipital foramen. 



In each somite of the thorax a distinct median sclerite, 

 the sternum, may be observed ; and a much larger tergal 

 piece, the notmn. At the sides of the somite are other defi- 

 nitely arranged sclerites, the anterior of which appear to an- 

 swer to the episternum and epimera in the Crustacea, while 

 the posterior, perhaps, properly belong to the attached limb. 



Forked or double apodemes, the antefurca, medifurca^ 

 and postfarca, project from the sternal wall of each somite 

 of the thorax into its cavity. They support the nervous cord 

 and give attachment to muscles. 



The legs present a large basal joint, the coxa, between 

 which and the third, termed femur, a small articulation, the 

 trochanter, is interposed. Upon the femur follows an elon- 

 gated tibia / and this is succeeded by the tarsus, which con- 

 sists of six joints. Of these, the proximal joint is long and 

 stout, the three next are short, the fifth is elongated and slen- 

 der ; the sixth, very short, is terminated by two curved and 

 pointed claws {ungues).^ 



1 Mr. "Westwoocl ("Modern Classification of Insects," vol. i, p. 416) says 

 that the tarsi are five-jointed, and that there is a pnlvilliis between the unffuea 

 The sixth joint appears to be what Mr. Westwood terms pvlviUnf^^ but it is a 

 true joint, provided with a special flexor, tlie slender tendon of which, how- 

 ever, traverses several of the joints of the tarsus. 



