PLATE XXIV. 

 THE DORSUM OF THE FOOT. 



The anterior annular ligament is divisible into two portions, an upper vertical* 

 which stretches across from the tibia to the fibula, and is merely a thickening in the 

 deep fascia ; and a lower or horizontal, which starts from the anterior rough upper surface 

 of the os calcis, and, passing as a strong band over the tendons of the extensor longus 

 digitorum and peroneus tertius, sends a strong slip behind them to reach the starting- 

 point at the os calcis : thus these tendons are enclosed in a pulley-like band. The rest 

 of the ligament is not so clearly defined, and consists of two parts, one of which passes 

 up over the extensor longus hallucis and then splits to enclose the tendon of the tibialis 

 anticus before its insertion into the tibia, while the other passes over both the extensor 

 longus hallucis and tibialis anticus to lose itself in the fascia over the inner side of the 

 foot. The pulley-like portion of the ligament is the only part of the lower band which 

 is repeated in most animals, and plays the same part there as in man. 



The extensor brevis digitorum is an interesting example of a migrating muscle, 

 shifting its attachment. This has been traced by Dr. Ruge. 1 In monotremes the muscle 

 arises entirely from the fibula, the belly for the tendon to the fifth toe being easily 

 separable from the rest, and having a higher attachment to the bone. In thylacine mar- 

 supials the whole muscle arises from the fibula, the tendons passing behind the external 

 malleolus, whereas in Didelphys cancrivora the belly for the great toe has descended 

 to take a pedal attachment from the os calcis, giving a small muscular slip to the short 

 extensor tendon of the second toe, which has its chief origin with the third and fourth 

 from the fibula, the fifth still being highest in origin and separated from the rest. In 

 cuscus and koala two bellies are pedal (2 and 8), and two fibular in origin the fourth 

 and fifth which still pass behind the malleolus to reach the foot. In carnivora both 

 the lion and the cat have three muscular bellies pedal in attachment springing from the 

 os calcis and annular ligament of the long extensor, the inner belly again splitting, 

 while the fifth still arises from a muscular belly high up on the fibula, and passes behind 

 the external malleolus to its insertion. In the monkeys, Ateles and Macacus rhtesus, 

 the fifth tendon is still arising from the fibula and passing down behind the external 

 malleolus in close proximity to the peroneus brevis, while the rest of the muscle is pedal. 

 In man there is a pedal extensor brevis sending tendons to the four inner toes, there 

 being no extensor (as such) to the fifth, but the peroneus brevis always sends forwards 

 a slip to join the extensor longus of the fifth digit, which it joins on its outer side : this 

 is probably the fifth tendon of the extensor brevis which in migrating has lost its 

 muscular mass, and whose sole remains is the tendinous slip blended with the peroneus 

 brevis ; it also throws light upon that muscular anomaly known as the peroneus 

 quinti digiti, which is probably a retrogression to the original condition. Dr. Ruge con- 

 siders that the outgrowth of the external malleolus in monkeys and man stops the further 

 distal migration of this muscle, which either perishes, as in the orang, or the belly of its 

 muscle becomes partially adherent with the peroneus brevis (as in cebus), or wholly 

 adherent, as in the chimpanzee, gorilla, and man. 



1 Uorph. Jahrbuch, 1878, p. 592. 



