Main features
Heart
This is a four-chambered pump lying in the cranial part of the thoracoabdominal cavity. It is covered in a pericardial sac which sticks to some of the internal surfaces to hold the heart in place.
Fig.
13.11 The avian c∣ncujtory 5y5iem.Circulation ι Hig. 1 3.11)
The arrangement of the arteries, veins and capillaries is similar to that of mammals with the following differences:
Rcnrely on the kidneys to regulate salt levels.
a yolk surrounded by several layers of cells. During the breeding season one ovum is released al approximately 24 hour intervals until Iheclutcli is complete.
Domestic poultry have been selectively bred to lay eggs over long periods - usually for 40 weeks per year.Wild birds will lay a clutch of eggs of a size appropriate to their species and then begin Incubation.