I have bought a fresh half leg of lamb today and there was a big disgusting green lump in the middle of it's fat. I'd like to know what it is and what should I do with the meat? Would anyone be able to help me please?  
I have sent the picture to the New Zealand Food Safety (NZFS) and asked them about it. This is their answer:  Thank you for contacting New Zealand Food Safety (NZFS) regarding your enquiry about the strange lump which you found in your piece of lamb meat. I have sent these photos to experts within the team who have looked over them. They have confirmed that it is most likely a lymph node, due to the grey/brown appearance and placement within the fatty area of the meat. Lymph nodes is considered a very normal element of the carcass and the ones seen in these pictures appear healthy. Unhealthy/abnormal lymph nodes (enlarged, hard, or full of pus) may have a very small risk if they were handed raw, but these would typically be discovered and removed by routine post mortem inspections. Because these lymph nodes appears healthy, the expert’s advice is that the meat is safe for consumption.  I have chosen this as the right answer, because it was a response from the officials, otherwise, @moscafj's answer was right. 