212 EVOLUTION AND DISEASE. 
In snakes the teeth do not come directly in contact: 
with the osseous tissue of the jaw; but, coincident with 
the development of the teeth, a formation of loose, bony 
matter occurs, whereby the base of each tooth is firmly 
cemented to the jaw-bone. Charles Tomes aptiy de-_ 
scribes this intermediate tissue as “bone of attachment”; 
it is of loose and open texture, resembling the alveolus. 
If from any cause this bone of attachment is softened or 
absorbed the teeth fall. It happens that snakes living 
in confinement are liable to a disease which induces” 
softening of the bones of the skull, and as the bone 
which attaches the teeth to the jaw is, especially when 
compared with the bones of the skeleton generally— 
which are of almost ivory-like hardness—soft, and easily 
absorbed, the snake in consequence loses its teeth. 
The relation of tooth, jaw, and bone of attachment is 
represented in fig. 113. Premature shedding of teeth 
from this cause is not infrequent in snakes living in 
captivity ; but I am unaware of its occurrence in snakes 
living wild. 
Absorption of the alveolus occurs in mammals as age 
advances, leading to the edentulous condition of the 
gums which is one of the concomitants of advanced life ;_ 
but the fall of teeth referred to in the case of the snake 
is due to constitutional defects, and not old age. 
