THE TONGUE 265 



organ. Coincident with the appearance of the adamantoblasts in 

 the enamel organ, the superficial cells of the dental papilla become 

 enlarged, elongated, and so arranged as to form a continuous layer 

 of odontoblasts on the surface of the papilla. These cells appar- 

 ently secrete a thin homogeneous layer, membrana praeformativa 

 (Raschkow), which serves as a basement membrane upon which 

 the adamantoblasts deposit the enamel prisms ; it also forms the 

 anlage of the granular layer of Thomes. 



The odontoblasts now form the dentine in a manner entirely 

 analogous to the deposit of bone by the osteoblasts, processes of 

 the odontoblasts being included within the deposit of dentine to 

 form the dentinal fibres. Irregular spaces, occurring in the den- 

 tine and granular layer, in which no calcification occurs produce 

 the interglobular spaces. 



The central mass of the dental papilla develops the embryonic 

 connective tissue of the tooth pulp. The blood vessels and nerves 

 enter the pulp through the base of the papilla, which thus becomes 

 the anlage of the root canal. 



The cementum is formed by intramembranous ossification oc- 

 curring in the connective tissue which invests the base of the 

 dental papilla and the primitive root of the tooth. 



THE TONGUE 



The tongue is formed by a reflection of the oral mucous mem- 

 brane which incloses a mass of muscular tissue. The fibres of this 

 striated muscle are separated into two lateral halves by a median 

 septum of dense connective tissue which extends from the base to 

 the tip of the organ, and is known as the lingual septum. 



The muscle fibres are disposed in three planes and are so ar- 

 ranged that the bundles cross one another at right angles. They 

 thus form : 1, saggital or vertical fibre bundles which are slightly 

 inclined outward from the septum linguae and are derived from 

 the lingualis muscle ; 2, longitudinal fibres running from the base 

 to the apex of the tongue, which are derived from the lingualis, 

 styloglossus, hyoglossus, genioglossus ; 3, transverse or horizontal 

 fibres extending laterally from the septum linguae, which are also 

 derived from the lingualis muscle. 



The interlacing bundles of muscle fibres are embedded in loose 

 areolar and adipose tissue. The muscle fibres are inserted into 

 the corium of the lingual mucous membrane, their sarcolemma be- 

 ing firmly adherent to the connective tissue of the mucosa, which 



