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,' 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,” 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,’ 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 
1M. pterygo-sphenoid posterior. 
2M. transverso-maxillo-pterygo-mandibularis. ‘This muscle aids in fastening the fang upon the prey 
attempting to flee. 
3M. pterygo-sphenoid anterior. 
4M. digastricus is held responsible by many writers for opening the mouth and lowering the mandible. 
