266 BULLETIN UNITED STATES GEOLOGICAL SURVEY. 



tissue, the outer of which gives off' three strong ligaments that hold it 

 in place. In a large snake, the entire gland may be nearly an inch long 

 and one-fourth as wide, weighing, empty, ten or twelve grains, and hav- 

 ing a capacity of ten or fifteen drops of fluid. There is no special reser- 

 voir for the venom, other than the central cavity of the gland. A certain 

 dilatation of one portion of the duct, formerly supposed to be such store- 

 house, is due to thickening of its walls, without corresponding increase 

 of capacity, resulting from muscular fibres which serve as a sphincter 

 to compress the canal and prevent wasteful flow of the contents. There 

 is further provision to this same end. When the tooth is folded back, 

 the duct attached to its root is submitted to some strain, which pushes 

 it against a shoulder of the maxillary bone, and tends to shut off the 

 communication. 



The injection of the venom, though to all appearance instantaneous, 

 is a complicated process of several rapidly consecutive steps. Forcible 

 voluntary closure of the jaws may always be, if desired, accompanied 

 by a gush of the venom, owing to the arrangements of the muscles which 

 effect such movement of the under jaw. These are the temporales, one 

 of the three of which is situated in such relation to the poison-sac that 

 its swelling in contraction presses upon the receptacle and squeezes out 

 the fluid. The force of ejection is seen when the serpent, striking wildly, 

 misses its aim ; under such circumstances, the stream has been seen to 

 spirt five or six feet. A blow given in anger is always accompanied by 

 the spirt of venom, even when the fang fails to engage, from whatever 

 cause. But since this result does not follow upon mere closure of the 

 mouth, it is probable that the two posterior temporals ordinarily effect 

 tills end, the more powerful action of the anterior temporal (the one 

 which presses upon the poison-sac) being reserved for its special purpose. 

 There is one very curious piece of mechanism to be noted here. Since 

 the serpent always snaps its jaws together in delivering a blow, the 

 points of the erected fangs would penetrate the under jaw itself in case 

 they failed to engage with the object aimed at, were there no contriv- 

 ance for preventing such disaster to the snake. But there is a certain 

 movement among the loose bones of the skull, perhaps not well made 

 out, the result of which is to spread the points of the fangs apart in 

 closure of the mouth, so that they clear the sides of the under jaw, in- 

 stead of impinging upon it. 



The complicated mechanism of the act of striking may be thus de- 

 scribed : — The snake prepares for action by throwing itself into a number 

 of superimposed coils, upon the mass of which the neck and a few inches 

 more lie loosely curved, the head elevated, the tail projecting and rap- 

 idly vibrating. At the approach of the intended victim, the serpent, 

 by sudden contraction of the muscles upon the convexity of the curves, 

 straightens out the anterior portion of the body, and thus darts forward 

 the head. At this instant, the jaws are widely separated, and the back 

 of the head fixed firmly upon the neck. With the opening of the mouth, 



