85 COMPARATIVE ANATOMY. 



I shall endeavour to poinfout other distinctions in the skulls 

 before us, and mention incidentally other characteristics 

 which my present specimens do not enable me to illustrate. 



The student who wishes to learn how to distinguish be- 

 tween the skull of one animal and another, would do well to 

 begin by learning carefully the names and positions of the 

 principal bones in a human skull, and although I would will- 

 ingly dispense with long scientific terms, if possible, I fear 

 that I must ask your careful attention while I name to you 

 one by one the bones of this disarticulated human skull 

 before me. 



(The lecturer here named the bones of the human skull). 



You are now in a position to compare these various bones 

 in the skull of man with the corresponding bones in other 

 animals ; but I must warn you of a difficulty that may at first 

 startle you, that in some animals you will find more, and in 

 some less than in man. This discrepancy will entirely vanish 

 if you make yourself master of the circumstances of the 

 developement of each bone. For instance, this Pterygoid or 

 bat-shaped bone that I am holding in my hand is really ten 

 bones ; that is to say it is developed from ten different centres 

 or points of ossification, which become united in the latter 

 period of the foetal state, or otherwise very soon after the birth 

 of an infant ; and in comparative anatomy all these bones 

 have names and are in certain instances found distinct. 



Again, the parietal and occipital bones which are not 

 united in the infant, producing thereby what you are familiar 

 with as the soft part of a baby's head, are in some animals 

 united at an earlier period of existence, and so grown to- 

 gether that they cannot be separated ; the suture or joint 

 having become entirely obliterated. 



But to turn to the teeth. All mammals have a definite 

 dental arrangement although in some cases that which is con- 

 sidered the regular formula is apparently violated ; nature 

 being a much less rigid systematist than man. 



Forty-four is considered the normal number of teeth in 

 the mammalia ; three animals alone representing it, viz., the 

 mole, the pig, and the gymnure. They are made up in the 

 following way: — In each half of each jaw there are three 

 incisors or cutting teeth, situated in the front of the mouth ; 

 one more pointed tooth called the canine or dog tooth ; four 



