332 



THE MAINTENANCE OF THE INDIVIDUAL 



procoroioidr 

 CoracoicC 



radius 



ScapLcla 

 glenoid -j^ssa 



xtlnct 



.carpccls 

 f ooi\. .■Tneta<;arpal 5 



The Appendicular Skeleton 



A study of any group of land animals shows a fundamental simi- 

 larity of limb construction. Even such apparently diverse structures 

 as the flippers of a whale or a seal and the wings of a bird are found to 

 be identical in fundamental plan. All sorts of land animals typically 

 possess shoulder and hip girdles, respectively known as pectoral and 

 pelvic girdles. These girdles are attached directly or indirectly to the 

 axial skeleton, thus providing rigidity and facilitating movement of 

 the appendages. It is significant that the pentadactyl limb of the 



land vertebrates is built 

 upon a generalized plan, 

 in which each girdle is 

 formed of three bones. 

 Each front and hind leg 

 is likewise composed of 

 three major bones. In 

 the anterior limb, a single 

 humerus articulates with 

 two bones, the ulna, a 

 process of which forms 

 the "funny bone " of the 

 elbow, and the radius. 

 In the posterior limb the 

 corresponding bones are 

 the femur, which is typi- 

 cally characterized by a 

 prominent "ball" at one 

 side of the main axis 

 fitting into a socket in 

 the pelvic girdle ; the 

 tibia, or shin-bone ; and 

 the smaller fibula. In 

 addition to these larger 

 bones is the group of 

 wrist {carpal) and ankle 

 (tarsal) bones, followed by the metacarpal and metatarsal bones, 

 depending upon whether they belong to the anterior or posterior 

 limb. The bones of the fingers or toes are technically known as 

 phalanges. 



•pre lirnb 



^ c c V 



...phoclanges 



femu"r 



pubis- 

 ischium 



tibia 



ODD tarsals 



f h '^ \ 

 I ;Br ■ 



Diagram of the bones of the fore and hind hmbs 

 arranged to show their homology. 



'\imd. HtoId 



--'pbalan^e-S 



