Boston round bottles were what Rene Caisse used to bottle up her Essiac decoction. Mary used to be the one that packed them for shipping to customers too far away to come by Rene's home to get their tea.
Both the 4 oz. (1/2 cup, or 120ml) and the 8 oz. sizes are good for the smaller pet-sized dosages, as the larger bottles may not all get used before the end of the typical shelf life of 2-4 weeks for an opened bottle.
The smaller bottles are also good for taking a few days' supply of Essiac on the road. Make your decoction with half the recommended amount of water. It will fit in bottles half the usual size. Cut your serving size in half (instead of 1 or 2 oz. per day, take 1/2 to 1 oz. - the decoction being twice as strong). The smaller jars take up half as much space.