HIND-LIMB. 149 



C. 211. Left hind-limb of Three-toed Sloth (Bradypus tridactylus) 

 showing the deeper muscles. The flexor digitorum (flexor 

 fibularis) is very large, it rises from the outer side of the 

 femur above the origin of the gastrocnemius (this part may 

 represent the plantaris) , and from a large part of the anterior, 

 inner, and posterior surfaces of tibia and fibula. The tibialis 

 anticus has a double origin, from the upper part of the tibia 

 and from' the lower half of the fibula (the second origin 

 may represent the extensor hallucis). Both portions are 

 inserted upon the inner margin of the entocuneiform. 

 This muscle has a powerful supinating action, turning the 

 foot into its usual climbing position with the sole towards 

 the mid-line. (See No. B. 187.) 



Humphry, Jour. Anat. & Physiol., vol. iv. 1870, 

 p. 17. 



C. 212. Muscles of the lower part of the left hind-limb of a 

 Two-toed Sloth ( Choloepus didactylus) . The two heads of 

 the gastrocnemius form distinct muscles with separate 

 insertions on the os calcis ; their tendons are longer than 

 in Bradypus, and cross one another before reaching the 

 heel. The tendon of the inner head is enveloped by the 

 soleus and soleal origin of the accessorius. The tibialis 

 posticus is double (an Edentate characteristic). A large 

 part of the tendon of the tibialis anticus passes round the 

 inner side of the foot and is attached to the flexor tendons, 

 by this palmar extension its rotary action must be con- 

 siderably increased, and at the same time additional power 

 of flexion given to the toes. 



Humphry, Jour. Anat. & Physiol., vol. iv. 1870, 

 p. 17. 



C. 213. Right hind-foot of Two-toed Sloth ( Choloepus didactylus) 

 showing the muscle insertions. The attachment of the 

 tibialis anticus to the flexor tendons and accessorius is 

 very clearly seen. The flexor tendons show a curious 

 bipenniform striation in their digital part. 



C. 214. Distal part of the right hind-limb of a Guinea-pig 

 (Cavia porcellus), showing the double origin of the tibialis 



