66 VENOMOUS SNAKES AND THE PHENOMENA OF THEIR VENOMS 



the squamosal bone is attached with the loose ligament. The squamosal 

 perhaps called mastoid bone by some authors is a flat, short oblong bone, 

 which attaches to the parietal (or temporal) region with the entire under 

 surface. At its posterior end it joints with the quadrate bone, which, in 

 turn, joints with the condyle process of the mandible. The quadrate is often 

 called zygoma. 



It may be stated that the lower maxillary bone of snakes consists of two 

 symmetrical halves, connected by a very strong ligamental band, and that it 

 is capable of a large amount of expansion. The occipital bone can not be 

 distinctly marked out, and this perhaps completely fused with the parietal 

 and temporal bones. 



Before entering on the description of the muscles which are concerned in 

 the mechanism of the erection of fangs, biting, and ejaculation of venom, it 

 must be stated here that the venom gland, in the majority of poisonous snakes, 

 occupies the space immediately behind the postorbital process (hence, the 

 posterior edge of the orbit) and the entire lateral region alongside the parietal 

 bone on each side. 



The erection of the fang is effected by the contraction of M. sphenoptery- 

 goid, 1 which originates in the crest at the base of cranium and, running 

 backwards and outwards, is inserted fan-like upon the pterygoid plate, which 

 is movable. 



The retraction of the fang is effected by the contraction of M. pterygoid 

 externus, 2 which arises from the tough aponeurosis covering the zygomatico- 

 mandibular articulation (or quadrato-mandibular) of the lower jaw, and, 

 running forward below the venom gland, is inserted tendinously into an 

 apophysis of the upper maxillary bone exteriorly to the maxillo-ectopterygoid 

 articulation. While passing below and inside the poison gland M. pterygoid 

 externus sends a strong layer of white fascial tissue out upon the capsule of 

 the gland. Some of its lower fibers are finally inserted directly into the two 

 lips or edges of mucous membrane of the fang. 



Another muscle, M. spheno-palatinus, 3 originates from the raphe of the base 

 of the skull, above the sphenopterygoid and thus nearer the skull, and, run- 

 ning diagonally outwards and backwards, inserts along the inside of the 

 palatal bone. As its fibers cross those of the sphenopterygoid, it has an 

 opposite effect to the latter, and thus assists the depressing action of the 

 pterygoid externus upon the fang. 



The opening of the mouth is effected by muscles, such as M. costo- 

 mandibular and M. vertebro-mandibular, with the help of a muscular layer 

 analogous to M. platysma myoides. The articulation of the jaw is fixed by 

 the double action of the digastricus 4 and cervical angular muscles. 



The closing of the mouth is effected by the temporal muscles. The most 



1 M. pterygo-sphenoid posterior. 



2 M. transverso-maxillo-pterygo-mandibularis. This muscle aids in fastening the fang upon the prey 



attempting to flee. 



3 M. pterygo-sphenoid anterior. 



* M. digastricus is held responsible by many writers for opening the mouth and lowering the mandible. 



