THE LIMBS. 175 



first phalanx (see Fig. 25, 10, p. 191). The obvious 

 mechanical use of this ligament (as it has now be- 

 come) is to prevent over-extension of the fetlock-joint. 

 If it is ruptured or stretched the animal becomes 

 what is termed in veterinary language "broken 

 down' 7 — i.e., the fetlock-joint sinks down, and the 

 hoof has a tendency to tilt forwards and upwards. 



" The most interesting point, however, in con- 

 nection with this structure is that it bears its history 

 on its face. Almost invariably two thin streaks of 

 striated muscular fiber are to be found on its super- 

 ficial surface, leading down to its two inferior divis- 

 ions. Again, on examining its deep surface, two 

 very distinct strands of pink fleshy tissue are always 

 observed extending throughout the entire length of 

 the ligament. These consist in each case of short, 

 oblique, striated fibers converging towards the mid- 

 dle line of the ligament. They represent those mus- 

 cular fibers of the two heads of the flexor orevis 

 which have not yet been converted into fibrous tis- 

 sue. On making a thin microscopic transverse sec- 

 tion the muscular fibers are seen to sink deeply into 

 its substance, but it is altogether so small in amount 

 in comparison with the bulk of the ligament that it 

 can exercise no function whatever." * 



* D. J. Cunningham, Zoology of the Voyage of H. M. S. 

 Challenger, Part XVI. Keport on the Marsupialia, p. 95. 



