FOEE-LIMB OF HOESE. 293 



only capable of a backward and forward movement, is articu- 

 lated by the head of the humerus with the pectoral arch at the 

 glenoid cavity. The humerus of the horse can be easily felt, 

 although it is hidden beneath the muscles and skin in the 

 " shoulder." This humerus is a short stout bone with two large 

 swellings, the trochanters ; the head is smooth and convex, and 

 the distal end marked by two grooves. The head and glenoid 

 cavity form a ball-and-socket joint ; the distal end and the 

 radius and ulna articulation form a hinge-joint, capable only of 

 a swinging motion. 



The forearm consists of two bones, the radius and ulna. In 

 man these two bones are quite distinct, but in the horse they 

 are united {It). The radius forms the chief bone articulating 

 with the distal end of the humerus and at its own distal end 

 with the knee-bones (K). The ulna is fused with the radius, 

 and terminates in a slightly swollen extremity about half-way 

 down the radius ; at its proximal end it rises above the radius 

 over the end of the back of the humerus, forming the olecranon 

 process. 



The radius articulates with the carpus or " knee " of the 

 horse. The knee (K) is composed of seven cubical bones, with 

 flat articulating surfaces arranged in two rows, forming three 

 distinct joints, one between the radius and first row, another 

 between the two rows of carpal bones, and a third between the 

 carpus and metacarpals. The bones of the two rows are the 

 unciform, magnum, and trapezoid, forming the lower row ; the 

 cuneiform, lunar, and scaphoid, forming the upper row ; and a 

 separate bone, the pisciform (Trap), behind. Sometimes there 

 is a fourth bone in the lower row, the trapezium.^ Each bone 

 has a delicate serous membrane surrounding it, the synovial 

 membrane, which secretes a lubricating fluid of a yellowish 

 greasy nature called synovium. This lubricating agent is not 

 an oil but an albuminous substance. 



^ The trapezium is a pea-like bone at the back of the knee, a vestigial 

 remains which I have never been able to find. — (G. T. B.) 



