THE FROG 



33 



The two long bones articulating with the processes of the sacral 

 vertebrae are the ilia. Each possesses a well- 

 marked crest, and unites with its fellow 

 posteriorly in the middle line to form a 

 part of the acetabulum. The remaining 

 part of the wall of this depression is 

 formed by two bones, in front by the small 

 pubis, which never completely ossifies, and 

 the larger posterior part by the bony 

 ischium. These three bones, ilium, ischium, 

 and pubis, meet the corresponding ones 

 of the opposite side in the middle line in 

 junctions termed symphyses. 



Before leaving the skeleton it will 

 be well to examine its structure in detail as 

 revealed by the aid of the microscope. Good 

 B 



cf 



_f 



QC. 



FIG. 7. A, Left hind limb Rana ; B, Pelvic girdle Rana viewed from 



right side. 



a., astragalus ; ac., acetabulum ; c., calcaneum ; ca., calcar ; d.t. t distal tarsalia ; /., femur; 

 i.e., iliac crest ; il., ilium ; is., ischium ; tnt., metatarsal ; p., phalanges ; pu., pubis ; t.f., tibio- 

 fibula ; I.~V., digits. 



examples of cartilage may be obtained by taking thin slices of the 

 head of a large bone, or of the epi- or xiphisternum, and examining 

 them in normal salt solution under the microscope. It consists of 

 a large number of slightly granular cells embedded in homogeneous 

 fairly clear substance, the matrix. The nuclei of the cells can be 

 readily made out ^by the addition of a drop or two of weak acetic 

 acid and of methyl green. This treatment also shows that a thin 

 layer of the matrix immediately surrounding the cell, termed the 

 capsule, stains more deeply than the rest. The cells, although some- 

 times single, are more often to be found in groups of two, three or 

 four, in each case derived from the division of a single cell. From the 

 fact that the matrix in these cases is very clear, the substance is 



D 



