8 PHYSIOLOGY' A NDTOXICO LOGY 



the two former bones must inevitably aifect the latter, and through it again the 

 maxilla and its single tooth.^ 



The motion of the maxillary bone on its lachrymal articulation will, perhaps, 

 be better understood upon reference to the accompanying diagram of the parts. 



Fig. 2. 



Diagram of the Bony Parts concerned in raising the Fang. — a, pterygoid bone ; /, m, arrow marking its line of 

 motion ; />, e, pterygoideus externus muscle ; g, frontal bone ; d, lachrymal bone ; c, superior maxillary bone ; 

 b, fang. 



The myology of the subject is more complicated ; yet even hei'e our purpose will 

 still be answered, if we describe only the muscles concerned, begging the reader to 

 remember that all further details would be misplaced and useless. On reference 

 to Fig. 3, it will be seen that the spheno-pterygoid, a, a strong muscle, arises along 

 the raphe at the base of the cranium, and running backwards and outwards, is 

 inserted fan-like upon the pterygoid plate. Acting from the fixed base of the 

 skull upon the movable pterj'goid bone, it must draw this bone forward, and, 

 rocking the superior maxillary on its lachrymal joint, erect the fang, Fig. 2, I — 7ii 

 and arrow. 



A second large muscle, the pterygoideus externus, Fig. 3, b, arises from the tough 

 aponeurosis covering the zygomatico-mandibular articulation of the lower jaw, and 

 as it runs forward below the poison gland and to its inner side sends a strong 

 layer of white fascial tissue out upon the capsule of the gland. Some of its lower 

 fibres are finally inserted directly into the two lips or edges of the mucous sheath 

 of the tooth fang. A larger part of the muscle is inserted tendinously into an 

 apophysis of the superior maxillai'y bone exteriorly to the articulation of that bone 

 with the external pterygoid, and a little below it. The mechanical necessities 

 arising from the position of this muscle are easily seen; for when the external 

 pterygoid acts, it will necessarily depress the fang. This movement will be more 

 readily comprehended on reference again to the diagram, Fig. 2, in the text, where 

 p — e marks the line of action of the force applied by the pterygoid muscle to the 

 superior maxillary bone and to the edges of the vagina dentis, the sheath of the 

 fang. The action of this muscle is probably aided by the spheno-palatine, which 

 arises along the raphe of the base of the skull, above the spheno-pterygoid and 

 thus nearer the skull, and running diagonally outwai'ds and backwards finds 



' These bones rest posteriorly against the articulation of the mandibulce of the lower jaw with the 

 zygoma ; they consequently share, to some extent, in the movements of this joint. 



