108 ANATOMICAL TECBNOLOBY. 



B. An excellent cement, for teeth especially, is the following : — 

 Silicate of soda or potassa (liquid glass) mixed to a paste with 

 powdered chalk. This hardens quickly, therefore it must be used 

 soon after it is prepared. Neither this nor the gelatin will resist 

 water. 



As soon as a macerated skull is rinsed, the teeth that are loose 

 should be taken out one at a time, the socket partly filled with one of 

 the cements and the tooth replauted. In this way the teeth may be 

 kept in their proper places, and as the skull dries the teeth will be 

 firmly fixed. Although the teeth of skulls prepared by the liquid 

 soap process may be loose before the skull is dry, the gelatinized 

 dental periosteum will usually fasten them very firmly as the skull 

 dries. If any of the teeth come out they should be replanted as 

 directed above. 



Need of Accuracy, — So far as concerns the general aspect of tlie skull, the incisors 

 may be intercbanged, and missing teeth may be replaced by teeth from other skulls. It 

 is to be feared that such substitutions are sonaetimes made with skulls prepared for sale. 

 Unless the changes are carefully specified, such skulls have no real scientific value as 

 regards the teeth. 



When two or more of the teeth drop out at the same time, unless direct observation or 

 comparison with a fresh or alcoholic specimen warrants absolute certainty, it is better to 

 keep those teeth in a box separate from the rest. 



§ 252. Preparation of Natural Skeletons. — By a natural 

 skeleton is meant one in which the bones are held together by their 

 natural ligaments. Such a skeleton may be prepared according to 

 either of the processes described above. One must, however, watch 

 that the ants may remove only the muscles, or that, in the process 

 of maceration, only the muscles decay. In all the processes, the 

 muscles are softened or removed first. If the liquid soap process is 

 employed, proceed as follows : Boil the bones in the mixture as 

 directed (§ 248) until the muscles may be removed without much 

 trouble. It wiU b§ found necessary, however, to allow the boiling 

 to proceed only to the point where the muscles will separate from 

 the bones by using the hands, a smooth stick like a scalpel handle, 

 or a dull knife blade. The ligaments will be found considerably 

 swollen and somewhat softened. The softened ectal surface maybe 

 cautiously scraped off; then the preparation should be soaked for 

 3-6 hours in a saturated solutipn of arseniate of soda (about 25 per 

 cent.), to poison the ligaments and protect them from Dermestes. 

 Then the part should be arranged as nearly as possible in a natural 



