288 ARTHUR D. WHEDON. 



divisions, the submentum and the mentum. The latter is some- 

 what the longer of the two, and is roughly spatulate in shape; 

 the former is subcylindrical. 



The mentum terminates apically in a rounded, median lobe which 

 bears a median notch and is edged with short bristles. On either 

 side of the median lobe is a lateral lobe bearing a moveable hook 

 and an end hook. These possess no muscles. Each lateral lobe 

 is hinged near the outer border of its base, while the medial lobe 

 is prolonged into a long triangular tendon which lies in a deep 

 slit-like imagination in the anterior edge of the mentum and re- 

 ceives the insertion of the adductor muscle. Proximally the 

 mentum narrows to a trifle more than half its apical width, and 

 deepens to accomodate the heavy adductor and abductor muscles. 

 It is hinged to the submentum as shown in the various figures, the 

 carinae being heavily chitinized. 



The submentum is flattened on the face opposed to the mentum, 

 otherwise it is nearly cylindrical. Its distal end is rounded and 

 projects beyond the hinge at which the mentum is received. It 

 is within this rounded, elbow-like projection (menton, of Amans) 

 that many of the important muscle attachments occur. The sub- 

 mentum is hinged closely to the ventral side of the head but pos- 

 sesses such freedom of movement as to enable it to swing in- 

 stantly from its normal position between the first and second pairs 

 of legs, when the labium is folded, to one in nearly the same plane 

 beneath and in front of the head. It is supported by the posterior 

 branches of the tentorium and surrounding skeletal parts. A 

 large outward fold between the head and base of the submentum, 

 supported by a T-shaped chitinous rod running forward and down- 

 ward to the base of the hypo-pharynx (ancre, of Amans), aids 

 in giving this freedom for the forwards thrust (Fig. i). Little 

 lateral movement is possible at this hinge and practically none at 

 that between the submentum and mentum. The submentum ac- 

 commodates two pairs each of extensor and flexor muscles. 



Larval Musculature. 



Muscles Activating the Lateral Lobes. The lateral lobes are 

 moved by two pairs of strong muscles, the abductors and the 

 adductors. 



