l8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 92 



44, functioning as the lateral adductor, corresponds to the primitive 

 muscle / with insertion on the upper anterior rim of the appendage. 

 The two remaining dorsal muscles, the minor abductor {42) and the 

 posterior adductor (^j) together represent the muscle /, since both 

 originate dorsally and are inserted on the posterior (now ventral !) rim 

 of the appendage. In the same way the muscle numbered 41, acting as 

 the major abductor, represents a combination of the ventrally-rising 

 primitive muscles K and L, since 41 is the only muscle of the appen- 

 dage having a ventral origin. 



41. Musculus abductor maior mandihidac (fig. 5 A, C). — Appear- 

 ing as a broad sheetlike muscle, this muscle originates in two places 

 on the head apodeme, and runs outward to its insertion along the 

 posterior part of the mandible, which it helps to open. 



42. Musculus abductor minor luaiidibulae (fig. 5 A. C). — This 

 muscle arises laterally on the dorsal head carapace on the inner part of 

 the epibranchial region and is inserted by a very slender but strong 

 tendon on the lower outer part of the mandible, which is opened by it. 



4J. Musculus adductor posterior mandihulac (fig. 5 A, C). — This 

 very strong muscle arises on the urogastric region of the carapace in 

 several heavy muscle bundles, which shortly fuse together into a long 

 and extremely heavy tendon that passes forward and downward to its 

 attachment on the mandible at the point of its lower articulation with 

 the head skeleton. It brings the mandible strongly toward the midline. 



44. Musculus adductar lateralis mandihulae (fig. 5 A, C). — This 

 extremely heavy muscle arises on the head carapace partly at the base 

 of the first spine and partly at the base of the third spine, the parts 

 uniting on a heavy tendon attaching them to the outer posterior end 

 of the mandible, which they bring strongly toward the midline. 



^5. Muscidus extensor palpi mandihulae (fig. 5 A). — This muscle 

 arises on the inner surface of the mandible near the base of the tendon 

 of the posterior adductor muscle. It is inserted on the heavy mem- 

 brane connecting the palp and the mandible, and its contraction 

 straightens the palp and brings it away from the center, opposing 

 flexor a in its action. There is no extensor for the distal segment of the 

 palp. 



46. Musculus flexor a palpi mandihulae (fig. 5 A). — This short but 

 stout muscle arises on the outer part of the mandible and travels for- 

 ward and slightly inward to its attachment on the posterior proximal 

 border of the first segment of the palp. Its function is to lower the 

 palp, thereby bringing it toward the median plane. 



