86 



hock-joint in the extended position, so far as to counteract the oscilla- 

 tions of the body, without the aid of muscular exertion ; and in this 

 respect it resembles the provision made to effect a similar purpose in 

 certain birds, as the stork, and some others of the grallae, which sleep 

 standing on one foot. It will appear, also, in the sequel, that not 

 only is the effect produced the same, but the mechanism is in many 

 respects similar, if the account given by Cuvier, and also by Dr. Ma- 

 cartney, in Rees's Cyclopaedia, article Birds, be correct. 



Sheep and cows are not provided with ankle-joints of a similar struc- 

 ture, audit is well known that tJiese animals do not possess the power 

 of sleeping standing. Another circumstance which adds additional 

 interest to this peculiarity of structure, is, that it may possibly be con- 

 nected with the disease termed String-halt, in which the limb is at 

 each step suddenly flexed, to a degree far beyond that required in 

 ordinary progression. Whether this is owing to a sudden and jerk- 

 ing flexion of the whole limb, or to flexion of the hock-joint alone, I 

 have had no opportunity lately of determining. If the latter be the 

 case, it is probably connected with the structure of the hock-joint, 

 which I am about to describe. It may be right to observe, that not 

 even a probable conjecture has been advanced, concerning the nature 

 and cause of string-halt, a disease to which the sheep and cow are not 

 subject, and we have already observed, that in these animals the struc- 

 ture of this joint presents nothing remarkable. 



The hock-joint is a good example of what is termed the hinge-like 

 articulation, and is formed between the tibia and astragalus, which 

 latter bone presents an articulating surface, with a nearly semicir- 

 cular outline, and divided into two ridges, including between them 

 a deep fossa. The tibia is furnished with depressions which ride 

 upon the ridges of the astragalus, and has anterior and posterior 

 projections, which, moving in the fossa, are received into corres- 



