Will discuss more next week. Sheep and cattle are ruminants with specialized four-chamber stomachs that also function as fermentation pouches to digest the cellulose in plants. 2 Circulatory system. In a fetus, the placenta is the site of gas exchange and not the lungs. Both of these close soon after birth.
Mammalian lungs are large and complex, with many clusters of alveoli.
The lungs are expanded by a muscular diaphragm between the thoracic and abdominal cavities. With the recoil of the diaphragm, exhalation shouldn't expend much energy. Mammals are endotherms , maintaining a high internal temperature by such means as shivering, as necessary. Hibernation or a slowed metabolism is an approach taken by many mammals around here for winter. 3 Mammals have a metanephric kidney, as do birds and reptiles.