164 couES, 



iilus where it crosses the median line. The insertion of this exten- 

 sive apparatus is rather difluse, and may not always be exactly as we 

 made it out in this specimen. Glutfeus proper becomes tendinous, or 

 rather fascial, dips among the tendons of the back of the leg just 

 above the heel, and thus has indefinite insertion, but is mainly pro- 

 longed over base of the spur, and heel, to be continuous with plantar 

 fascia. The caudal part, on the other hand, has definite insertion into 

 the tibia; twisting for that purpose, much as latissimus or pectoralis 

 major does, so that the most anterior fibres (those that give off the 

 intertibialis) are inserted lowest down. The insertion is in the mid- 

 dle third of the tibia behind, for about half an inch, opposite the in- 

 sertion of the gracilis. The plantar attachments doubtless cause the 

 muscle to act somewhat as an extensor of the foot — in obvious sub- 

 serviency to advantageous action in giving the back-stroke. 



(b'. — From the pelvic arch : " long.") 



Biceps. — The external or fibular flexor cruris is a single-headed 

 broadly triangular muscle, without femoral origin. It arises definitely 

 from the tuber ischii, at first overlaid by the ectoglutseus ; as it 

 emerges from under which, it rapidly widens into a broad and com- 

 paratively thin plane that spreads over nearly all the leg, in apposi- 

 tion, at first with the tibial flexores cruris that also arise from the 

 ischiatic tuberosity, and afterwards with the great fibular head of 

 the gastrocnemius and other peroneal muscles. Partly in conse- 

 quence, very likely, of the burial of the fibula in muscle, the biceps 

 has no actual insertion into that bone, except just at the upper mar- 

 gin of the spatulate peronecrauon. Muscular fibres terminate, in a 

 curved line corresponding to the outer border of the calf of the leg, 

 in a broad dense aponeurosis that sweeps over and envelops the 

 whole front of the leg, with final definite insertion into the crest of 

 the tibia from the patella two-thirds way down the leg, besides send- 

 ing below sundry fascial prolongations between the tendons of an- 

 terior tibial muscles. This actual insertion of the outer (fibular) 

 flexor cruris into the innei- bone of the leg occurs in marsupials also, 

 as, for instance, in the DideJ.pliys virginiana, where it oflers a highly 

 interesting analogy to the ulna?- insertion of one foot of the biceps 

 brachii of the same animal. The actions of the Ornithorhynchus' 

 biceps cruris are several ; firstly, it retroducts the femur and extends 

 the whole limb ; secondly, it is a flexor of the leg ; and thirdly, it is a 

 powerful external rotator of the limb below the knee, turning the 

 heel directly towards, and the claws away from, the body. The 

 mechanism of the knee-joint, as explained below, allows this action, 

 which is furthered by the way the aponeurotic tendon of insertion of 

 the biceps laps over the swelling muscles of the calf, as a band over 

 a pulley. 



