66 Prof. A. Macalister on the Myology o/Bradypus tridactylus. 



nenm. The soleus or fibular head arises from the upper fourth 

 of the back of the fibula, and is inserted beneath the last named. 

 The inner head is the largest, the external second in size, and 

 the soleus smallest of all. The external is the largest in the 

 Dasypus. There are no sesamoid bones in the origins of the 

 muscle, as there are in the Tamandua and Myrmecojjhaga 

 didactyla. Meckel, however, refers to the Ai as possessing one 

 of these in its origin ; and in the Megatherium one of these ap- 

 pears to have existed for the outer head of the gastrocnemius. 

 The soleus does not arise from the middle of the fibula, a& 

 stated by Cuvier, but is limited to its upper portion alone. 



The popliteus muscle is large and possesses a large sesamoid 

 bone in its tendon of origin. As usual this muscle runs from 

 the outer condyle of the femur to the back of the tibia. It 

 does not seem to possess a sesamoid bone in the Tamandua, 

 OrycteropuSj or Dasyjnis. 



Plantaris is a large pear-shaped muscle arising above the 

 outer head of the gastrocnemius ; and, passing down the poste- 

 rior surface of the leg, it ends in a tendon which is inserted 

 into the tendon of the flexor digitorum longus. This digital 

 continuation seems to be characteristic of the plantaris in the 

 Edentate animals, as it likewise exists in the Six-banded Ar- 

 madillo and in Orycterojyus capensis. Rapp makes no men- 

 tion of it as present in the Tamandua ; but possibly he may 

 have confounded it with the gastrocnemius. This muscle 

 seems to me to be larger proportionally in the Sloth than in 

 any other animal that I have dissected. 



Flexor digitorum longus arises from the posterior surface of 

 the tibia, and is inserted into the three toes by three strong- 

 tendons. Its tendon is strengthened in the middle of the sole 

 of the foot by the plantaris, which unites with it as a strong- 

 accessory. In the Orycterope this muscle is fibular in its origin 

 (Galton, p. 596), and sends a tendon to all the toes, even the 

 hallux, and receives a slip from the tibialis posticus to assist 

 it in forming- the tendon for this digit. This muscle is like- 

 wise mainly fibular in its origin in the ArmadiUo, and pos- 

 sesses a plantar ossicle. 



Flexor hallucis longus, a very large muscle, arises from the 

 fibula and interosseous membrane, passes downwards for a 

 short distance, and unites with the last-described muscle to be 

 inserted in common with it into the toes. 



The tibialis posticus is very small and inconspicuous ; it 

 passes from the lower half of the back of the tibia, and is 

 inserted into the inner cuneiform bone of the tarsus. 



There are two musculi accessorii in the foot, one from the 

 outer and the other from the inner surfaces of the calcaneum : 



