lOO 



THE COMMON FROG. 



[chap. 



fibres enclosed, assume the forms of cones. Moreover, 

 the apices of the membranes enclosing the cones, 



Fig. 63. — Superficial Muscles of Extensor Side of Leg and of parts of Trunk and 

 Tail of Menopoma. ES, erector spinse — directly continued into dorsal half of 

 tail ; ELD, extensor longus digitorum pedis ; FC, femoro-caudal ; GM.x, pro- 

 bably rectus femoris ; /, muscle resembling iliacus ; ILC, ilio-caudal ; IP, ilio- 

 peroneal ; KF, part of great extensor of thigh ; SM and ST, muscles like the 

 semi-membranosus and semi-tendinous. 



become denser in substance, and so modified into 

 ligaments.^ 



We come thus to have a key to the process of 

 development, by which the muscles of the back may 

 be conceived to have arisen. 



The muscles of the back may be conceived as 

 having arisen through increasing obliquity, conical 

 prolongation, and partial detachment (from muscle) of 

 the separating membranous lamellae ; the produced 

 ends becoming condensed into firm tendons directed 

 more or less obliquely forwards. 



