i8 



ANATOMY OF THE RABBIT 



(c) Tarsus 



6 tarsals 



I calcaneum 

 I astragalus 

 I navicular (scaphoid) 



I second cuneiform 

 I third cuneiform 

 I cuboid 



4 metatarsals 



4 digits 



12 phalanges 

 4 proximal 

 4 middle 

 4 distal (ungual) 



7 ossa tarsaha 

 I calcaneus 

 I talus 



I OS naviculare pedis 

 I OS cuneiforme primum 

 I OS cuneiforme secundum 

 I OS cuneiforme tertium 

 I OS cuboideum 



(d) Metatarsus 



5 ossa metatarsalia 



(e) Digits 



5 digites 



14 phalanges digitorum-pedis 

 5 phalanges d.p. prima 



4 phalanges d.p. secunda 



5 phalanges d.p. tertia 



B. DEVELOPMENT AND CLASSIFICATION OF BONES 



The process of ossification is essentially one of impregnating 

 connective tissue with calcium salts by the activity of special- 

 ized connective tissue cells, called osteoblasts. From the 

 manner of calcification, bones are of two principal kinds: (i) 

 Direct, intermembranous or dermal bones are thin bones, 

 such as form most of the sides and top of the cranium and the 

 greater part of the face. In this type osteoblasts deposit the 

 calcium salts directly in young connective tissue without 

 the bone being first preformed in cartilage. These are called 

 membrane bones because they are developed within sheets of 

 embryonal connective tissue membrane. They are sometimes 

 called dermal bones because they are represented in some of the 

 lower vertebrates by dermal plates. (2) Indirect, endochronal, 

 cartilage or replacing bones are preformed in fetal cartilage and 

 this cartilage is in turn replaced by calcium salts to form the 

 bone. Areas of calcium deposition are called centers of 

 ossification. There are often three or more centers of ossifica- 

 tion in each developing bone, the carpals and tarsals have only 



