1909] Anatomy and Relationship of spiders 19 



and join in the tibia those fibres which arise by means of a tendon 

 from the proximal hypo-edge of this latter segment. Together 

 they form the i. — M. flexor metatarsi longus (Fig. 3. B.. m. 1.) 

 which is inserted with a long tendon into the middle of the proxi- 

 mal hypo-edge of the metatarsus. 2, M. flexor metatarsi bilobatus 

 (Fig. 3. fl. m. b.) is composed of two symmetrical halves and arises 

 from the entire episynaxial surface of the tibia. Its numerous 

 short tendons are inserted closely together on both sides of the 

 tendon of the long flexor. The description of this muscle given 

 by Gaubert is entirely wrong and I am not able to comprehend 

 what has brought him to the conclusion that its point of 

 insertion is on the dorsal (episynaxial) surface of the metatarsus 

 and that this muscle is therefore an extensor. There is no exten- 

 sor of the metatarsus. 



Metatarsus. Enclosed in the metatarsus are two muscles, 

 one of which is the antagonist of the other, i . M. flexor unguium 

 (Fig. 3. fl. u.) arises from the proximal surface of the metatarsus 

 and receives additional fibres w^hich arise from the distal end of 

 the episynaxial surface of the tibia. Its long, thin tendon tra- 

 verses the metatarsus and tarsus and is inserted into the base of 

 the claws. 2, M. extensor unguium (Fig. 3. ex. u.) arises from the 

 proximal epi-edge of the metatarsus and is inserted by means of 

 a long and thin tendon which runs above and parallel to that 

 of the flexor into the base of the claws above the latter. 



Tarsus. The tarsus has no muscles and encloses merely the 

 two tendons above mentioned. 



In reviewing the muscular system of the legs in spiders w^e 

 observe that its characteristic feature is the absence of extensors 

 in the majority of segments. Only the coxa and the metatarsus 

 enclose extensors.^ The function of the extensors is evidently 

 transferred in the other segments upon the hypodermis forming a 

 thin elastic membrane over each joint. The homology of the 

 muscles enclosed in the femur and tibia is too apparent to admit 

 of doubt, and I believe that it can be extended to the muscles 



I. In the second volume of his text-book of experimental zoology, which has 

 just appeared, Przibram reproduces Fredericg's diagram of the muscular system 

 of a spider-leg. Evidently misled by Garber's old interpretation of the muscular 

 system of appendages in Arthropods, he figures a flexor and an exten.sor in every 

 segment of the limb. However, even a superficial examination of the articulations 

 cannot fail to show that his supposed extensors are in reality flexors. If he had 

 noticed that the axes of the patellar and metatarsal articulations lie not on the 

 ventral side of the limb, but in its epis3naxial (dorsal) surface, he would have 

 escaped this error. 



