354 NAVIN ON THE HORSE. 



The icpper arm-hone, or humerus, is a rather short, thick and 

 heavy bone, belonging to the class of long bones, having a body 

 and Uyo heads. Its upper head is large and round and is re- 

 ceived into the cavity of the lower end of the shoulder-blade. 



Its lower head is large and very broad, and marked by a 

 deep o-roove from before backward, and which terminates be- 

 hind fn a deep pit, or excavation. This groove receives a cor- 

 responding ridge, running in the same direction of the head ot 

 the larger arm-bone, or radius, the next bone below it I he 

 pit or excavation, at the back end of the groove is for the pro- 

 iectino- portion of the small arm-bonc, called the elbow, to rest 

 in The humerus is marked by several eminences for the at- 

 tachment of muscles, and has attached to it the principal 

 ^muscles engaged in sustaining and lifting the weight of the 



'horse 



The upper head of the humerus rests in the shallow cavity of 

 ithe shoulder-blade, and is held in place by a strong elastic liga- 

 .ment surrounding its head, and fastened all around the margin 

 ,of the shallow socket of the shoulder-blade. This bone stands 

 in an oblique direction, downward and backward, from the 

 •shoulder-joint. In a well-formed horse this bone should be 

 short, and incline well back. If long, the shoulder will be too 

 ■upright, and the weight of the horse too far forward. But for 

 .heavy draught this objection is not serious. 



The shoulder-joint is seldom liable to dislocation, but may 

 .suffer from bruise, by the horse plunging against a solid object. 

 The bone could hardly be fractured. 



The arm-bones are two in number; the larger called the 

 Tadius, the smaller the ulna. They are distinct bones, united 

 ^by cartilage until advanced age, when the cartilage becomes 

 •ossified and the two bones become as one solid bone. 



The radius, or larger arm-bonc, has a long shaft or body, 

 •smooth before and rough behind. It has two heads, the up- 

 :per marked by a high ridge from before backward, on each 

 .side of which is an excavation, or cavity. The ridge fits into 



