76 



ZOOLOGY 



SECT. 



by cartilage bones, the lasalia (Bas\ which serve to strengthen the 

 fin at its point of union with the trunk. 



In all classes above Fishes the paired fins are, as we have seen, 

 replaced by five-toed or pentadactyle limbs. These are supported by 

 bones, probably to be looked upon as greatly modified pterygiophores, 

 and obviously homologous in the fore- and hind-limbs. In the proxi- 

 mal division of each limb there is a single rod-like bone, the humerus 

 (Fig. 722, A, HU), or upper arm bone in the fore-limb, the femur 

 (B, FE), or thigh bone in the hind limb. In the middle division 

 there are two elongated bones, an anterior, the radius (RA), 

 and a posterior, the ulna (UL), in the fore-limb ; an anterior, the 



SCP 



B 



FIG. 722. Diagrams of the fore (A) and hind (B) limbs with the limb-girdles, actb. acetabulum : 

 grLglenoid cavity ; p. cor. procoracoid ; / V, digits. Cartilage bones cn.l, en. 2, centralia : 

 COR. coracoid; dst. 15, distalia ; FE. femur; FI, fibula; fi. fibulare ; HU. huinerus : 

 III. ilium ; int. intermedium; IS. ischium ; mtcp. 1 5, metacarpals ; mt.ts.l 5, 

 metatarsals ; ph. phalanges ; PU. pubis ; RA. radius ; ra. radiale.; TI. tibia ; ti. tibiale ; 

 UJL. ulna ; ul. ulnare. Membrane bone CL. clavicle. 



tibia (TI), and a posterior, the fibula (FI), in the hind-limb. 

 Next follow the bones of the hand and foot, which are again 

 divisible into three sets : carpals or wrist-bones, metacarpals 

 (mtcp) or hand-bones, and phalanges (ph) or finger- bones, in the 

 fore-limb ; tar sals or ankle-bones, metatarsals (B, mtts) or foot 

 bones, and phalanges (ph) or toe-bones, in the hind-limb. The 

 carpals and tarsals consist typically of three rows of small nodules 

 of bone or cartilage, the proximal row containing three, the middle 

 two, and the distal five elements. The three proximal carpals are 

 called respectively radiale (A, ra), intermedium (int), and ulnare 

 (ul), those of the middle row the first and second centralia (en. 1. 



