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sighthound
Sighthounds, also called gazehounds, are hounds that primarily hunt by sight and speed, instead of by scent and endurance as scent hounds do.
==Appearance==
These dogs specialize in pursuing prey, keeping it in sight, and overpowering it by their great speed and agility. They must be able to detect motion quickly, so they have keen vision. Sighthounds must be able to capture fast, agile prey such as deer and hare, so they have a very flexible back and long legs for a long stride, a deep chest to support an unusually (compared to other dogs) large heart, very efficient lungs for both anaerobic and aerobic sprints, and a lean, wiry body to keep their weight at a minimum.
The typical sighthound type has a light, lean head, which is dolichocephalic in proportion. This shape can create the illusion that their heads are longer than usual. Wolves and other wild dogs are dolichocephalic or mesaticephalic, but some domesticated dogs have become brachycephalic (short-headed) due to artificial selection by humans over the course of 12,000 years. Dolichocephalic breeds have a wider field of vision but smaller overlap between the eyes and therefore possibly poorer depth perception in some of their field of view than brachycephalic breeds; most, if not all, dog breeds have less visual acuity than their antecedent the wolf.
There is no science-based evidence to confirm the popular belief that sighthounds have a higher visual acuity than other types of dogs. However, there is increasing evidence that dolichocephalic breeds, thanks to a higher number of retinal ganglion cells in their “visual streak”, retain more heightened sensitivity than other breeds to objects and rapid movement in the horizontal field of vision.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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