2. All viviparous quadrupeds have an œsophagus and trachea, situated as in man, and so have oviparous quadrupeds and birds, though there is some difference in the formation of these parts; all that breathe by inhaling and exhaling air have lungs, trachea, and œsophagus. The position of the œsophagus and trachea, though similar, is not the same, nor are the lungs alike in all, nor similar in position. 3. All sanguineous animals have a heart, and a division in the middle of the body, called a diaphragm. In small animals its smallness and thinness render it less apparent. The heart of the ox is peculiar; for there is a kind of ox, though not the whole genus, which has a bone in its heart, and there is also a bone in the heart of the horse. 4. Not all animals have lungs, fish and those with gills have no lungs. All sanguineous animals have a liver, generally a spleen also; but in oviparous animals that are not viviparous, the spleen is so small as nearly to escape notice, as in most birds, the pigeon, kite,[58] hawk,[59] and owl. The ægocephalus[60] has none at all. Oviparous quadrupeds are of the same nature, for they have a very small spleen, as the tortoise, emys,[61] phryne, lizard, crocodile, and frog. [58] Falco milvus. [59] Falco palurabarius. [60] Stryx otus. [61] Testudo coriacea. 5. Some animals have a gall upon the liver, others none. Among viviparous quadrupeds the stag[62] has none, nor the deer,[63] horse, mule, ass, seal, and some swine. The Achaïnian stag appears to have the gall in the tail; that which they call gall in these animals resembles it in colour, but it is not liquid like gall, but more like the spleen in its internal structure. [62] Cervus elaphus. [63] Cervus capreolus, or C. Dama. 6. All, while they are alive, have worms[64] in the head; they are produced in the hollow part under the hypoglottis, and near the vertebræ, where the head is joined on. In size they resemble very large maggots; they are numerous, and continuous, in number not generally more than twenty. Stags, as I have observed, have no gall, but their intestines are so bitter that dogs will not eat them if the deer are fat. [64] Possibly Œstras nasalis.