The BBC has a picture to illustrate it, and Animal Domain also has a summary.
There are now 340 individual mountain gorillas in the park, up from 320 in 2002. The numbers of this critically endangered group have been declining precipitously because their habitat is being destroyed and also due to poaching and their lack of resistance to human diseases.
Mountain gorillas also inhabit the Virunga Volcanoes on the borders of Uganda, Rwanda and the Democratic Republic of Congo. A 2003 census of these gorillas counted 380 individuals.
Currently there are 720 mountain gorillas worldwide.