314 VEKTEBliATE ANIMALS. 



forniubi for tlie portion f>f tlie jaw of the Chimpanzee figured above 

 (tig. 224) would be as follows : — 



(' 2 ; t' 1 ; 2"!^ - ', '" •'^■ 

 But this is only one half of the lower jaw, and the dental formula 

 must include both sides, so that it would be : — 



i2 — 2; fl— 1; /,m 2— 2 ; v/t 3— 3. 



That this would be the fornnila is at once eviilent, when it is 

 I'eniembered that the two sides of the jaw of course contain e.xactl}' 

 the same teeth. Still, the formula as given aboA'e oidy includes the 

 lower jaw, and to render it perfect it mu.st take in the teeth of the 

 upper jaw a.s well. This is effected by jjlacing the figures in two 

 rows se]iarated by short lines, all the figures in the ripper row 

 referring to the \ipper jaw, and those in the lower row to the lower 

 jaw ; the short dashes between the figures of each row still indi- 

 cating tlie teeth on the two sides of the mouth. The complete 

 formula would therefore run as follows : — 



.2—2 1 — 1 2—2 3—3 



I - ; <■ ; nni ■ rii = 32. 



2—2 1 — 1 ^ 2 — 2 3—3 



In this way the deutition — that is to say, the n\iml,)er and arrange- 

 ment of the teeth — can be presented in a maimer which can be 

 instantly lecogiiiseil by the eye. It must be remembered, however, 

 tliat the formula seldom exhibits the regularity of the one of the 

 ('him|ianzee given above. The teetli are not nece.ssarily the same 

 ill both jaws, and in many cases some may be altogether wanting. 

 To show this there is subjoined the dental formula of a typical 

 Ruiuinant aiiinial, such as a sheep : — 



From this fcinnula it will be seen that the sheep has 32 teeth ill 

 biith jaws taken tiigi'ther. The U|>per incisors and canines are 

 wanting, and tliei'c a,re three jira'iiidl.ars and three molars on each 

 side of the upper jaw. In the lower jaw there are six incisors, 

 two canines, anil the same number of ])i';riniilars and nuilars as in 

 the up])er jaw. 



As regards the digesti\e system of Mammals, the alimentary 

 canal and digesti\'B glands h.-ne on the whole the .same general 

 structure and arrangement as in man (p]i. 223, 224). Some very 

 remarkable modillcatioiis, however, in the .structure of the stomach 



and in the termination of the intcsline, air in cerl.aiii Mammals ; 



but these will lie noticed ill speaking of the orders in which thev 



