368 



REPORT OF NATIONAL :MUSEUM, 1893. 



RAlIilNO 



Fijr. 10. 



DIAGRAM OF THE BONES CONCERNED 

 THE FAXfi. 



rt Pterygoid bone; l-m arrow marking its lint- 

 ofmotioii ; jD-t'exteniiil pterygoid iriiiscle; g frontal 

 bone ; (/ lachrymal bone ; c maxillary bone ; b fang. 



( Aft^r M.ti-h.'ll. ) 



The taii.u' itself is a large, very pointed, and curved tooth containing 

 two cavities, the pnlp cavity and the iwison canal, the toriner situated 

 on the concave side, the latter on the convex side of the tooth (tig. iM)). 

 The poison canal has a more or less slit-shaped opening near the base, 

 on the anterior side of the fang, and another slit, narrower and longer 



on the same side, some little dis- 

 tance from the very sharply 

 pointed ti]). Between these open- 

 ings it is often possible to trace a 

 more or less well-defined depressed 

 line. A microscopic inspection of 

 cross sections of the fang reveals 

 the fact that the canal is nothing 

 but a deep groove, the walls of 

 which have closed over it ante- 

 riorly, the depressed line indicating 

 the meeting of the walls, or the 

 " seam." This structure of the fang 

 may be easily understood by com- 

 paring it to a leaf curling up in drying, the edges meeting and over- 

 lapping in the middle, leaving an upper and a lower opening. By making 

 sections <»f growing and full-grown fangs of the same individual, the 

 evolution of the grooved fang into the " perforated" fang is easily traced, 

 and the inexactness of the latter term clearly demonstrated. As a 

 consequence of this origin of the canal, it is lined with the same hard 

 layer of dentine as the outer side of the fang, for it will be seen that 

 this inner lining of the canal is in reality the 

 anterior surface, while the outer layer is only 

 the i)OSterior surface of the normal tooth. An 

 inspection of the accompanying figure (fig. 17), 

 which represents a cross section through the 

 upper jaw, with the functional full-grown fang 

 followed l)y the moreor less uiuleveloped reserve 

 fangs, will show this plainly, as the same prin- 

 ciple is involved in the Pit Vipers. 



As already stated, the fang is above fixed 

 firmly in the socket of the maxillary bone, ''its 

 base being luted to the portion of the bone 

 around its side and anterior aspect," to borrow 

 Dr. Weir Mitchell's words.* "Posteriorly, the 

 bone possesses a hollow, in which is lodged the 



tooth sac. In the open mouth of this alveolar process, within the mucous 

 membrane, and upon the pterygoid bone, lie one behind and below 

 another, the reserve fangs, each smaller than the one in front and less 



Fig. 17. 



A.^fiAXGEMENT OF THE RESERVE 

 fANUS IN BUNGARUS SEMIFAS- 

 CIATUS, ILLUSTRATING THE DE- 

 VELOPMENT OF THE GROOVED 

 FANG INTI ) THE CANAI.ED FANG. 



Eulari;<-,1. 



* Researches upon the Veuoiu of the Rattl.-snakt^ 

 Knowledge. Washiugtou, 1861, p. Ui. 



Siiiithsoniau Coutrihutioiis to 



