REPORT ON THE SPHENISCID^. 125 



below the origin of the popliteus, from the middle third of the inner surface of the same 

 bone, from the whole length of the posterior border of the fibula, and from the 

 interosseous membrane. The muscular fibres immediately above the ankle joint give 

 place to a tendon which, after perforating the fibro-cartilage behind the ankle joint, 

 divides into three slips. These, after uniting with the corresponding slips derived from 

 the tendon of the first or femoral head of the muscle, pass forwards, to be inserted into 

 the terminal phalanges of the second, third, and fourth toes. They perforate the tendons 

 of the flexor perforatus to the same toes. 



Action. — This muscle flexes the toes. 



Relations. — The first or femoral head of origin of this muscle lies under cover of the 

 flexor perforatus, and rests upon the second or tibial head. The second head rests upon 

 the tibia and fibula, from which bones it arises. 



Nerve supply. — Both heads are supplied by branches from the sciatic nerve. 



Variations. — In addition to the three tendons above described, I found in Spheniscus 

 demersus, Spheniscus mendiculus, Sphenisctis magellanicus, and Eudyptes chrysocome from 

 the Falklands, a fourth very delicate slip, which was given ofi" from the tendon of insertion 

 of the second head of this muscle. This minute tendon passes along the under surface of 

 the first or rudimental toe, and is inserted into the terminal phalanx of that digit. 



In Spheniscus 'magellanicus the femoral head of the muscle takes an additional 

 attachment to the upper extremity of the fibula. 



In Pygosceles tceniatus the tendon of insertion of the femoral head unites with that of 

 the tibial head, previous to the sub-division of the latter into its three slips. 



RemarJcs. — Gervais and Alix describe the femoral head of oriwiu of this muscle under 

 the name of " fl^chisseur du pouce." As already observed, it undoubtedly represents that 

 muscle, but by reason of the rudimentary condition of the hind toe in the Penguins, 

 instead of being chiefly attached as in many birds to that toe, it incorjiorates itself with 

 the tendon of the second or tibial portion of the muscle, which in other birds exclusively 

 represents the flexor perforans. In Eudyptes chrysolophus, according to Gervais and 

 Alix, the tendon of the flexor perforans does not give off" any slip to the rudimental toe. 

 That slip, according to these authors, is replaced by a tendinous band, which passes 

 between the sheath of the flexor perforans and the second phalanx of the rudimental toe. 



9. Flexor hrevis hallucis. 



FlecMsseur du doigt poster ieiir, Vicq d'Azyr, 1774, p. 517, No. 1. 



Der Daumenbeuger, Wiedemann, p. 106. 



Der Beuger des Daumens, Tiedemanu, p. 345, No. 9. 



Mttsele No. 4, Meckel, vol. vi. p. 126. 



Flexor of the thumb, Reid, p. 145. 



Court Jleddsseur du pouce, Gervais and Alix, p. 38. 



