Having just finished Yoma- Daf Yomi, I am left with one question that does not seem to be resolved in the Mesechta. In the Avodah of slaughtering the bull, the Cohen Gadol starts the Shechita, cutting most of the oesaphagus and trachea, then someone else finishes the Shechita while he catches the blood. The problem I have with this is the issue of how he could catch the first part of the Dam Hachaim. The first part of his cut is simple - it is just blood from the skin and thus can fall to the ground, the cut across the two vessaels seems more problematic as surely that blood is going to be flowing fast and thus he would have to be moving a vessel to catch it within a few seconds of the cut- and in many places in the Mesechta there is a concern that the Cohen Gadol is weakened from blood loss, and surely this would be very difficult if not impossible to do in a weakened state.
I am no expert in anatomy, but give over to you the matter as explained in the edition of Masechet Yomah put out by Machon Hamikdash. The Cohen Gadol makes the minimal cut (most of 2 Simanim) which does not yet cause profuse bleeding. The knife is given to another Cohen, the CG takes the utensil for receiving the blood, the other Cohen continues the cut and opens the arteries so the blood flows easily. According to Tosefot Yeshanim, the CG could theoretically do this by himself, but we are worried that in his weakened state he would find it too difficult.