LECTURES ON HORSES. 491 
already illustrated by comparisons between the upright shoulders 
of dray-horses, and the oblique ones of thorough-breds. 
Let us now pass to 
THE ARM. 
Anatomists and horsemen will find themselves at variance con- 
cerning the part to which this appellation is applied. The anato- 
mist regards the humerus as the bone of the arm : the horseman 
calls that part “ the arm ! ” which extends from the elbow to the 
knee ; and incongruous and, to the anatomist, confusing as these 
appellations, arm and knee , are, yet has custom so established 
their use among horse people that we dare not refuse to adopt them. 
The horseman’s arm, consequently, becomes the anatomist’s fore- 
arm: the humerus or proper arm being incorporated with the 
shoulder, from the circumstance of the horse not being provided, 
as a man, and a monkey, and some other beasts are, with those 
little bones whose use is to set the arms off from the shoulders — 
the clavicles or collar-bones. 
The arm of the horse, the same as our own fore-arm — to which, 
I repeat, it corresponds — has in its composition two bones, the ra- 
dius and the ulna ; but with this difference, that in man and the 
monkey, and also in some quadrupeds, the ulna is a separate bone 
of equal length with the radius ; whereas in the horse it is nothing 
more than an attachment to the radius, the medium of union be- 
tween them being in the young animal, and indeed up to the adult 
period, an elastic (cartilago-ligamentous) substance, which yields to 
force, and thus in action serves the purpose of a spring diminishing 
concussion. Indeed, this appears to have been one reason why the 
ulna was not extended to the knee-joint : had it been a separate 
bone no such spring could have existed. At full growth, however, 
or very soon after, the uniting elastic matter becomes converted into 
bone, consolidating the ulna with the radius, and for ever destroying 
the original spring. 
At the superior part the ulna enters into the composition of the 
elbow-joint., the same being the part which protuberates backward 
and forms the elbow. Thus placed and fashioned, the ulna answers 
two important uses : one is, extension of the surface of the joint 
and limit to its motion backward, by serving as a stop to it ; the 
other is the leverage it offers for the insertion of muscles whose 
office is to extend the fore-limb. The advantages derived from 
long and prominent elbows are precisely such as ^re afforded by 
length of lever in any situation out of the body : providing the 
weight to be lifted and the lifting forces to remain the same, the 
power of the latter will be increased in direct ratio with the length 
of the lever — the elbow ; and considering that the operation of 
these muscles though immediately upon the arm, extends all the 
