54 TEE ANATOMY OF YERTEBKATED ANIMALS. 



The flexor carpi racUalis is also roughly represented by the 

 tibialis posticus — a muscle which passes from the tibia and 

 interosseous membrane to the entocuneiform, and therefore 

 differs in insertion, as well as in origin, from its analogue in 

 the fore-limb. The flexor perforatus digitorum of the foot 

 takes its origin sometimes from the calcaneum ; sometimes, in 

 part from the calcaneum, and in part from the perforating 

 flexor ; or it maybe closely connected with the tendons of the 

 p)lantaris. T\\e p)eronce%is hrems represents the ^ea^or carp>% 

 ixlnaris by its insertion, but it arises no higher than the fibula, 

 and has no sesamoid. 



Two most important muscles 3^et remain to be considered 

 in the leg. The one of these is that which is inserted by the 

 tendo achillis into the calcaneum, and arises by four heads, 

 two from the condyles of the femur (called gastroc72emius), 

 and two from the tibia and fibula (called soleus). The other 

 muscle is the ^^ero^zcpws ^o??^i^5, arising from the fibula, pass- 

 ing behind the external malleolus, and then crossing the foot 

 to the base of the metatarsal of the hallux. 



The latter muscle does not appear to have any representa- 

 tive in the fore-limb. The gastrocnemius and salens may pos- 

 sibly represent the cruj-al part of the perforated flexor, since, 

 in many of the Vertehrata^ the tendo achillis is but loosely 

 connected with the calcaneum, and passes over it into the 

 plantar fascia and the perforated tendons. A peculiar adduc- 

 tor muscle of the hallux in Man and Apes is the traoisversalis 

 p)edis^ which is inserted into the basal phalanx of the hallux, 

 and arises from the distal ends of the metatarsals of the 

 other digits. The muscle sometimes has an analogue in the 

 manus. 



Electrical Organs. — Certain fishes belonging to the gen- 

 era Torpedo (among the Elasmohranchii)^ Gynmotus, Ma- 

 laptemriis^ and Mormyrus (among the Teleostei)^ posses 

 organs which convert nervous energy into electricity, just as 

 muscles convert the same energy into ordinary motion, and 

 therefore may well be mentioned in connection with the ner- 

 vous system. The " electrical organ " is alwaj's composed of 

 nearly parallel lamellag of connective tissue, enclosing small 

 chambers, in which lie what are termed the electriccd ptlates. 

 Tliese are cellular structures, in one face of which the final 

 ramifications of the nerves, which are supplied to the organ 

 by one or many trunks, are distributed. The face on which 

 the nerves ramify is in all the plates the same, being inferior 

 in Torpedo^ where the lamellae are disposed parallel to the 



