J. Playfair McMurrich 45 



Gadow, 82, and Perrin, 93, both describe this muscle as a portion of 

 the flexor longus digitorum (flechisseur des quatre premiers doigts), 

 that is to say of the plantaris profundus IIl-II, making it a femoral head 

 of that muscle. It may be that it is really a portion of the plantaris 

 profundus group of muscles which has secondarily extended its origin 

 to the femur and that its absence in Ophryoessa and Cnemidophorus, 

 as noted by Gadow, is due to this upward migration not having taken 

 place. On the other hand it seems more probable that the origin from 

 the femur is a primary condition, the muscle being a separation of 

 the deeper portions of the plantaris superficialis lateralis. Its union 

 with the plantaris profundus presents no more obstacle to this view than 

 the similar union of the superficialis tenuis; both the plantaris profun- 

 dus and the plantaris superficialis insert primarily into the plantar 

 aponeurosis, so that a union of the two sets of muscles is not at all im- 

 possible. On account of its associations with the deep plantar muscles 

 it will be spoken of as the plantaris superficialis accessorius. 



The plantaris profundus group of muscles is represented in the lacer- 

 tilia by three distinct muscles, one of which is to be regarded as repre- 

 senting the plantares profundi III and II of the amphibian crus, while 

 the other two represent the plantaris profundus I. The plantaris pro- 

 fundus III-II (Fig. 4, Pp^^'^^^) is the muscle termed by Gadow the 

 flexor longus digitorum, caput internum, and by Perrin the tete interne 

 du flechisseur des quatre premiers doigts. It takes its origin from the 

 upper half of the fibula and to a slight extent from the outer surface of 

 the head of the tibia, and increases rapidly in size as it descends the 

 crus, forming the most voluminous muscle of the calf of the leg. At 

 about one-third of the length of the crus an aponeurotic layer appears 

 upon its posterior surface (Fig. 4, a') and into this the plantaris super- 

 ficialis accessorius and the plantaris superficialis tenuis insert. As it 

 approaches the ankle joint the aponeurosis increases in strength and be- 

 comes tendon-like, the fibres of the muscle terminating upon it, and at 

 the ankle joint a sesamoid bone (Fig. 5, s) is developed upon its tibial 

 border, the last remaining muscle fibers and also the plantaris profundus 

 I accessorius inserting into this. With the development of the sesamoid 

 bone the whole aponeurosis or tendon becomes thick and almost carti- 

 laginous, but as it is traced onward into the foot it again becomes ten- 

 dinous and gives off a slip from its fibular border. This passes to the 

 fifth digit, sending off a slip to the fourth, and the main portion of the 

 tendon passes on beneath the superficial muscles of the planta to divide 

 eventually into tendons which pass to the three inner digits. All the 

 five tendons pass to the terminal phalanges of their respective digits and 

 give origin in their course to the lumbrical muscles. 



