OF COLYMBUS TOEQUATUS. 171 



proceeds to the head of the metatarsal bone, just over which it splits into two for the mid- 

 dle and outer toes. The tendons extend to the bases of the last phalanges on each toe. 



Peroneus. Much smaller than either of the others, this muscle arises from the fibula for 

 the greater part of its length. Its tendon passes through a separate canal in the annular 

 ligament, on the outer aspect of the joint, and proceeds obliquely backwards, to be inserted 

 into the posterior border of the metatarsal bone, just at its base. From the peculiar posi- 

 tion of the tendon where it is bound down, as well as by its insertion, it can have little or 

 no effect in moving the tarsus backwards or forwards. When the tarsus is extended it may 

 weakly aid in extending it ; but its principal office is evidently to direct and restrict the 

 rotatory movements of the tibip-tarsal joint. It quite powerfully rotates it outwards, and 

 antagonizes the tibialis posticus on the outer side of the joint. 



Gastrocnemii. In the gastrocnemii there is seen the same plan as was noticed in the 

 " triceps" extensor cubiti, viz. — a tendency to divide into two distinct muscles. It is not, 

 however, so strongly pronounced as in the former instance, though the three origins of the 

 gastrocnemius are even more widely diverse. 



The inner, or rather the anterior gastrocnemius lies upon the inner and anterior aspect of 

 the tibia for its upper two thirds, afterwards crossing the leg obliquely, to get upon its pos- 

 terior aspect. It has two heads ; one arising fleshy from the apex of the tibial spine, from 

 the whole anterior face of the upper two thirds of the bone, and from the fibrous septa 

 between it and other muscles ; the other from the inner condyle of the femur ; tlje ten- 

 dons of the semi-tendinosus and scmi-membranosiis being interposed between them. 



The posterior or outer gastrocnemius arises from the " linea aspera " for nearly two thirds 

 its length, and from the outer condyle ; also receiving attachments from the muscle 

 described as the rectus femoris. 



These two portions of the muscle, thus diversely arising are fleshy to within two inches 

 of the heel. There they change into two stout round tendons, entirely separate from 

 each other. A little above their final insertion they fuse into one broad, thick, very power- 

 ful tendon, which passes directly over the posterior aspect of the joint, (overriding the 

 tendons of the other muscles,) and is inserted into the base of the bony protuberance on 

 the back of the metatarsus. 



At the mesial edge of the insertion of the last described portion of the gastrocnemii, 

 there proceeds down from the femur a most perfect sample of an aponeurotic loof). This 

 loop encircles the tendon of the biceps flexor cruris, and changes the direction of its line of 

 traction as much as does the loop which in our species binds down the tendon of the 

 digastricus to the hyoid bone. It runs down from the femur as a distinct narrow fibrous 

 band ; embraces the tendon, and returns upon itself, the two ends of the loop being in- 

 serted side by side. This loop is more or less blended with the fibrous investment of the 

 under surface of the gastrocnemius. 



The dissection and examination of the remaining muscles of the back of the leg is ex- 

 ceedingly difficult. They are all more or less intimately united with each other, throughout 

 the greater part of their muscular as well as tendinous structure. They arise from the outer 

 and posterior aspects of the bone, and from the intermuscular septa between one another. 

 They become tendinous at very various points. Their tendons, however, are all aggregated 

 together to pass directly over the posterior aspect of the heel. Just over the joint, nearly 

 all are enclosed in one large dense shiny white mass of fibro-cartilage, through which each 

 tendon bores a canal for itself. Leaving this sheath, all but one (the tibialis p)osiicus ?) 



MEMOIK3 BOST. SOC. NAT. HIST. Vol. I. Pt. 2. ** 



