While mounts such as Apollo and mercury, can all be traced back to having placement at the base of each finger, the lower Mars mount exists between the thumb and index finger. This is not the webbing or just the small area of skin, but it takes up a generous amount of space in itself. All of this information is necessary in order to get a really accurate reading of what you are seeing when you look at your palm. Too short, and you may miss something crucial, but too long, and the lower mars mount may have extended already into the plane of mars.
The mounts are considered very important in understanding palms because of the interplay that they have with the different main lines. Some of the main lines intersect with some of the mounts and that alone can give off very useful information to a palm reader. Sometimes the mounts do not intersect with any of the lines at all, but they can still give information to the palm reader based on how prominent their presence is on the hand. For example, a raised mount of mercury that takes prominence over the other mounts on the hand would suggest good communication skill.
In regards to the lower mars mount though, if this were a mount that was more prominent on a hand that you were reading, then this would mean that you are a tenacious person, or that you are aggressive and demanding. The aggression that the lower mars mount is indicative of is not necessarily negative, or the kind that should be hidden from the public. A better word to describe it might be courage. Mars was the god of war, so naturally anything that he represents, or that represents him, will be related to war and aggression.
This can also just mean that you are a driven person. These people generally turn out to be more successful in life, but it is a toss-up. A good way to tell if your driven attitude will consume much of your life or not, is to see how your life line intersects with the lower mars mount. The life line is in the perfect position to intersect with the lower mars mount. Thus, if your life line does intersect with the lower pars mount, it means that aggression will become a large part of your life. This does not necessarily indicate your level of future success, but it does show that you will certainly be more predisposed to using your natural attitude and your own beliefs to get ahead in life or to reach new heights. While this may not apply to your career necessarily (unless the fate line intersects with the lower mars mount as well) it will still mean that your life will revolve around your strong will and desires.