in PRACTICAL DIRECTIONS 53 



tied in a knot. This shows that the bone contains a 

 large amount of organic or animal matter. On the 

 other hand, a bone may be completely calcined by heat- 

 ing to redness in a closed vessel, when its animal matter 

 is completely consumed and its mineral matter left. 

 Under these circumstances it becomes very brittle, 

 falling to pieces at a touch, and its appearance is far 

 more altered than by the removal of the mineral matter. 



PRACTICAL DIRECTIONS 



Preparation of the Skeleton. Kill a frog with chloroform 

 (p. 31), open the abdomen as directed on p. 32, but without 

 cutting the shoulder-girdle, and remove the contained 

 organs. Then, the frog being firmly pinned down, remove 

 the skin and gradually cut away the flesh from the bones. 

 In the case of the long bones of the limbs, it is best to cut 

 through the muscles near one end of the bone and then 

 gradually to strip them back towards the other end until 

 the bone is exposed. The process is facilitated by dipping 

 the frog occasionally into boiling water (maceration in 

 cold water requires a considerable time) : this softens the 

 connective-tissue by which the bones and muscles are 

 bound together, and thus allows them to be more readily 

 separated. While at work keep Fig. 8 before you, and be 

 particularly careful not to injure those parts of the skeleton 

 which are made of cartilage (dotted in the figure), and are 

 therefore easily cut : the most important of these parts are 

 the hyoid or tongue-cartilage lying in the floor of the mouth, 

 the omosternum, the xiphisternum, and the supra-scapula 

 (Fig. 12). Great care will also be required in cleaning the 

 bones of the hands and feet, since the fine cords or tendons 

 which pass to them from the muscles are very strong, and 

 if pulled upon with much force are sure to bring away the 

 small toe-bones with them : they should be separated as far 

 as possible and then cut off, close to the bones, with scissors. 



Keep all the parts of the skeleton together, avoiding 

 separation of the various bones, until the general charac- 

 teristics of the entire skeleton have been made out : the 

 only part which cannot be kept in connection with the rest 

 is the shoulder-girdle, together with the fore-limbs. 



Examination of the Skeleton. You should have two 

 skeletons to examine one dried, after it has been thoroughly 



