"■ PRACTICAL DIRECTIONS 53 



completely calcined or heated to redness in a closed vessel, 

 when its animal matter is completely consumed and its 

 mineral matter left. Under these circumstances it becomes 

 very britde, 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 according to the directions 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 with scalpel and scissors. 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 : this softens the connec- 

 tive tissue by which the bones and muscles are bound together, and 

 thus allows them to Ije 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 lartilage (dotted in the figure), 

 and are therefore easily cut. The most important of these cartilaginous 

 parts are the Ityoid or tongue-cartilage (b.hr), lying in the floor of the 

 mouth, the oinosteriudii (Fig. 12, in front of .£/), which projects in 

 the middle line in front of the shoulder-girdle, and the xiphislerttum 

 (Kit), which extends backwards from the same region. 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 «ith 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 characteristics of the entire skeleton 

 have been made out : the only part which cannot be kept in connection 

 with the rest is the shoulder-girdle, which will come apart, together with 

 the fore-limbs. 



Examination of the Skeleton.— Vou should have two skeletons 



to e.xaraine — one dried, after it has been thoroughly cleaned, and one 



