Hi Blue.
In reference to my post about venomous snakes closing the jaw to squeeze the venom out of the venom gland, it was merely an attempt to keep the explanation in as simple terms as possible so that the average punter has a chance to interpret the information provided.
It is true that your reference to page 15 of Rick's book explains that the masseter muscle attached to the rear of the venom gland contracts to squeeze the gland and force the venom through the deliver system but it does not explain the mechanics of how the masseter muscles operate. The same explanation in duplicated on pages 304 and 305 of "Herpetology: An Introductory Biology of Reptiles and Amphibians" Laurie J Vitt & Janalee P Caldwell.
This muscle is only a thin membrane located underneath the venom gland. Does it work independently and is it able to be individually controlled by the snake? What mechanics actually cause the muscle to contract? Feel free to correct me if I'm wrong but I believe it just may be attached to other muscles that are connected with both the upper and lower jaws.
Vitt and Caldwell state that venomous snakes can also regulate the amount of venom delivered in a bite by contracting the adductor superficial muscle (connected at the rear of the venom gland) however; again there is no explanation of how the mechanics of an elapid snake bite works.
Kenneth V Kardong's paper "Lateral Jaw and Throat Muscles of the Cottonmouth Snake" explains that along with the masseter muscles the adductor superficial muscles found in elpaid snakes are also instrumental in squeezing the rear of the venom gland to distribute it along the delivery system. These muscles are located at the junction on each side of the upper and lower jaw, and further explains that lateral jaw movement is controlled by the lower jaw. He states that the contraction of the "Modelius compressor grandulae muscle is implemented in venom ejection due to its close association with the venom gland but may likewise be partnered with other muscles in jaw closure".
To me this further suggest that it is highly likely the amount of pressure applied by the lower jaw at the time of a bite has a direct effect on the amount of venom delivered in a bite.
Now in saying all this and considering that elapids tend to either bite their intended victim/prey in a deliberate hard biting action and/or maintain a grip on same to inject sufficient quantities of venom to immobilize their prey it is more than likely a that a choice has been made by the snake to bite hard in such a situation and thus apply sufficient pressure on all the muscles mentioned to deliver the quantity of venom determined to immobilize and subsequently kill the item being bitten.
To me. whether this is a conscious choice to choose the amount of venom delivered or simply an act of instinct appears to be open to debate.
I don't know about you but I have personally experienced both wet and dry bites from small Australian elapids as well as a dry bite from a Death Adder and full envenomation form a Red-bellied Black, Tiger Snake and Brown Snake. I can assure you that on each occasion when I have been envenomed I felt a notable difference in the amount of pressure applied by the snake's upper and lower jaws when it is a deliberate and intentional bite compared to when I have suffered a dry bites which (at least in my case) have always occurred where the snake has failed obtain contact with its bottom jaw.
So it would appear to me that it is a reasonable assumption that to add to all the other possibilities that may contribute to a dry bite, it may be possible that what I have outlined may just be another contributing factor to the discussion.
I reiterate that based on personal experience and from what I have read this is just my personal assumption of how a dry bite may occur.
George