THE FROG 5 1 



indicating that the bone is made up of concentric layers, 

 called lamellae. At the periphery find an epithelial layer 

 (how many cells in thickness?) called the periosteum; this 

 is often injured in the process of preparing the sections. 

 Observe that the marrow consists mainly of loose connective 

 tissue traversed by blood vessels; there is a dense accumu- 

 lation of rounded cells with large nuclei just within the bony 

 layer. Under high power, sketch a portion of a section ex- 

 tending from the center to the periphery. 



Examine a cross-section of dry bone taken from some 

 mammal; how does it differ from the bone of the frog? 



The various parts of the skeleton are either immovably 

 fastened together, or connected in such a way as to allow 

 some freedom of movement; in either case the connection 

 is called an articulation or joint. Where slight movement 

 is required, the bones are united by pads of tough and elastic 

 fibre-cartilage, as in the joints between the bodies of the 

 vertebrae; in the more movable joints, each articular surface 

 is covered with a pad of cartilage, and the bones are held 

 together by strong bands or capsules of fibrous material, 

 called ligaments. 



With the aid of the following outline, study both articu- 

 lated and disarticulated skeletons of the frog, and be pre- 

 pared to demonstrate all the bones, both in the articulated 

 and the disarticulated preparations. 



The skeleton of the frog may be conveniently divided 

 into: (a) the axial skeleton, including the skull and the 

 vertebral column, and (&) the appendicular skeleton, in- 

 cluding the limbs and the limb girdles which attach them to 

 the body. What evidence of metameric segmentation do 

 you find in the skeleton of the frog? 



