J. Playfair McMurrich 41 



Plautaris suiierticiiilis inediulis, ^ 



Plautaris superlicialis lateralis, „ ^ • i- i- i- 



,-, . . ' . , y.T )■ Ramus superticiahs medialis. 



Plantans iiroiundus III, ' 



Plantaris profundus II, J 



Fibulo-tarsalis, Ramus superlicialis fibularis. 



Plantaris profundus I, 1 r> r i 



T , y Ramus profundus. 



Interosseus, J ' 



II. The Crural Flexors in the Lacertilia. 



A goodly number of papers dealing with the myology of the hind limb 

 of members of the group Lacertilia have appeared, that of Gadow, 82, 

 being one of the most comprehensive. It has been the custom, however, 

 to employ for the various muscles a terminology based upon that used 

 for the mammalia, a procedure which carries with it implications of 

 homologies which in some cases do not exist and in the majority of cases 

 are at best merely partial ones. Since in the present study the lacer- 

 tilian myology is being approached from below, rather than from above, 

 and since in the amphibia the characteristic feature of the crural muscles 

 is their arrangement in layers, I propose to employ for the reptilian 

 muscles a terminology which will indicate their relations to the amphi- 

 bian condition, using the terms employed by Gadow, for instance, only 

 for purposes of identification. 



A transverse section through about the middle of the crus of Scincus 

 presents the appearance shown in Fig. 3. At first sight the differences 

 from the arrangement in Amblystoma are very apparent, but a closer 

 inspection will reveal marked similarities, which a study of the nerve 

 supply will but serve to emphasize. The topographical relations of the 

 muscles may, however, first be considered, with a view to determining 

 how far a layered condition can be recognized. 



It is a characteristic of the amphibian superficial plantar layer that it 

 arises from the femur and is inserted below into the plantar aponeurosis. 

 In Scincus one finds superficially upon the posterior surface of the crus 

 three muscles, a plantaris superficialis medialis {Psm), a plantaris 

 superficialis lateralis (Psl), and between the two a long slender muscle 

 which may be termed the plantaris superficialis tenuis (Pst). Of these 

 the plantaris superficialis medialis differs from the other three in that it 

 arises from the head of the tibia, instead of from the femur as might be 

 expected if it be really a portion of the superficial plantar layer. Ex- 

 amining its origin more closely it will be seen to arise not only from the 

 head of the tibia but also from the posterior surface of a strong tendon 

 which passes from the head of the tibia to the internal condyle of the 

 femur. The existence of this tendon and the relation of the muscle 



