AN INTRODUCTION TO ZOOLOGY 



Appendicular Skeleton. 



The skeleton of the fore-limb consists of a number of bones, 

 which may be divided up in the same way as the limb itself. Inside 

 the brachium is a single bone, the humerus, which 

 serves as a good example of what is known as a 

 long bone, and is divisible into a proximal part, 

 i.e. the end near the body called the head, a long 

 middle part the shank, and a distal portion the 

 condyle. Like all the bones of the limbs it is a 

 cartilage bone, and its two ends, termed epiphyses, 

 ossify separately from the shank, with which they 

 afterwards fuse. The head of the humerus is 

 rounded and covered with articular cartilage. 

 From its head a strong keel, the deltoid ridge, 

 runs along the front side of the shank. The 

 distal end has two prominent lateral condylar 

 ridges, between which is a depression, the tro- 

 chanter, in part filled with a knob covered with 

 articular cartilage. The skeleton of the anti- 

 brachium consists of a bone, the radio-ulna, 

 formed by the union of two separate bones, the 

 radius and ulna, showing distinct signs of its 

 double origin. Its proximal end is hollowed to 

 receive the humerus, and it projects backwards 

 beyond this as the olecranon process. At its 

 distal end it articulates with a series of six wrist 

 bones, or carpalia. The first row consists of 

 three bones called the radiale, the intermedium, 

 and the ulnare. The first and last are situated 

 at the ends of the radial and ulnar parts of the 

 combined bone, and the intermedium lies between 

 F IG . 5 . Longitu- them. The second row als'o consists of three 



dmal section of bones, two small ones and a larger posterior one, 

 the femur, show- .. ,, . , . ., 



ing the compact representing three smaller ones fused together. 



and cancellous Following this comes the skeleton of the manus. 



tissues, and the j ne p rox i ma i p ar t consists of a row of five small 



medullary cav- . 



ity. From Fur- bony rods, the metacarpals. The anterior of 



neaux. " these is smaller than the rest, and is all that re- 



mains of the first digit, the pollex or thumb. The 

 other metacarpals are followed by a varying number of small rods, 

 the phalanges. Two are borne on the first or fore-finger, two on the 

 second, and three each on the third and fourth. When a limb is 

 stretched out the side on which the big toe or thumb is situated 



