|
Dog anatomy includes the same internal structures that are in humans. Details of structures vary tremendously from breed to breed, more than in any other animal species, wild or domesticated,〔(Scientists fetch useful information from dog genome publications, Cold Spring Harbor Laboratory, December 7, 2005; published online in Bio-Medicine ) quote: "Phenotypic variation among dog breeds, whether it be in size, shape, or behavior, is greater than for any other animal"〕 as dogs are highly variable in height and weight. The smallest known adult dog was a Yorkshire Terrier, that stood only at the shoulder, in length along the head-and-body, and weighed only . The largest known dog was an English Mastiff which weighed and was from the snout to the tail.〔(【引用サイトリンク】title=World's Largest Dog )〕 The tallest dog is a Great Dane that stands at the shoulder. ==Physical characteristics== Like most predatory mammals, the dog has powerful muscles, a cardiovascular system that supports both sprinting and endurance, and teeth for catching, holding, and tearing. The dog's ancestral skeleton provided the ability to jump and leap. Their legs can propel them forward rapidly, leaping as necessary to chase and overcome prey. Consequently, they have small, tight feet, walking on their toes (thus having a digitigrade stance and locomotion); their rear legs are fairly rigid and sturdy; the front legs are loose and flexible, with only muscle attaching them to the torso. The dog's muzzle size will come with the breed. The sizes of the muzzle have different names. Dogs with longer muzzles, such as the German shepherd dog, are called mesocephalic and dogs with a pushed in muzzle, such as the pug, are called brachacephalic. All dogs (and all living Canidae) have a ligament connecting the spinous process of their first thoracic (or chest) vertebrae to the back of the axis bone (second cervical or neck bone), which supports the weight of the head without active muscle exertion, thus saving energy.〔Wang, Xiaoming and Tedford, Richard H. Dogs: Their Fossil Relatives and Evolutionary History. New York: Columbia University Press, 2008. pp.97-8〕 This ligament is analogous in function (but different in exact structural detail) to the nuchal ligament found in ungulates.〔 This ligament allows dogs to carry their heads while running long distances, such as while following scent trails with their nose to the ground, without expending much energy.〔 Although selective breeding has changed the appearance of many breeds, all dogs retain the basic characteristics of their ancestors. Dogs have disconnected shoulder bones (lacking the collar bone of the human skeleton) that allow a greater stride length for running and leaping. They walk on four toes, front and back, and have vestigial dewclaws on their front legs and on their rear legs. When a dog has extra dewclaws in addition to the usual one the rear, the dog is said to be "double dewclawed". The dog's ancestor was about the size of a Dingo, and its skeleton took about 10 months to mature. Today's toy breeds have skeletons that mature in only a few months, while giant breeds such as the Mastiffs take 16 to 18 months for the skeleton to mature. Dwarfism has affected the proportions of some breeds' skeletons, as in the Basset Hound. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Dog anatomy」の詳細全文を読む スポンサード リンク
|