CHAPTER IX 
THE DENTITION, ALIMENTARY CANAL, AND DIGESTIVE GLANDS 
THE alimentary canal is a muscular tube with an epithelial 
lining, formed for the reception and the digestion of the food. 
It begins with a mouth, and from thence it extends backwards 
through the coelom, finally communicating with the exterior 
either by a cloacal or by an anal orifice. The oral or buccal 
cavity into which the mouth leads is a stomodaeum, and is lined 
by inpushed epidermis, while the hinder portion of the cloaca 
and the anus are lined by a somewhat similar inpushing of the 
epidermis which forms the proctodaeum. The rest of the 
alimentary canal, consisting in succession of a pharynx, an 
oesophagus, a stomach, and an intestine, constitutes the mesen- 
teron, and is lined by endoderm. Teeth are developed from the 
walls of the stomodaeum, and glands for the secretion of digestive 
fluids from the endoderm of the mesenteron. 
Dentition. 
In the Lampreys among the Cyclostomata teeth are developed 
in the form of yellow conical structures on the inner surface of 
the buccal funnel, and on the extremity of the rasping “ tongue” 
(Fig. 91, A). Each tooth consists of an axial papilla of the 
dermis, sometimes enclosing a pulp-cavity, and invested by 
the epidermis, and also by a stratified horny cone which forms 
the projecting hard part of the tooth. The dermal papilla with 
its ectodermal investment bears a superficial resemblance to the 
germ of a true calcified tooth, but no odontoblasts are formed, 
nor any calcic deposit, the laminated horny teeth being formed 
by the gradual conversion of the successive strata of the 
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