骨格の考察5

ヒトの脊椎骨は、頭蓋骨の後頭骨にある大後頭孔より下降し、骨盤に至る。脊椎は、頸椎（cervical、7椎、まれに8椎）、胸椎（thoracic、12椎）、腰椎（lumbar、5椎）、仙椎（sacral、5椎）および尾椎（coccygeal、3-6椎）の約30個の椎骨から形成されている。骨と骨は関節でつながっており、その間にはクッションの役割をする椎間板がある。

Wiki

In human anatomy, the vertebral column usually consists of 24 articulatingvertebrae,^[1] and nine fused vertebrae in the sacrum and the coccyx. It is situated in the dorsal aspect of the torso, separated by intervertebral discs. It houses and protects the spinal cord in its spinal canal, and hence is commonly called the spine, or simply backbone.

There are normally 33 vertebrae in humans, including the five that are fused to form the sacrum (the others are separated by intervertebral discs) and the fourcoccygeal bones that form the tailbone.

The upper three regions comprise the remaining 24, and are grouped under the names cervical (7 vertebrae), thoracic (12 vertebrae) and lumbar (5 vertebrae), according to the regions they occupy. This number is sometimes increased by an additional vertebra in one region, or it may be diminished in one region, the deficiency often being supplied by an additional vertebra in another. The number of cervical vertebrae is, however, very rarely increased or diminished.^{[citation needed]}

胸骨（きょうこつ、英語：sternum）は人においては胸郭前面の正中部にある扁平骨であり、上から胸骨柄・胸骨体・剣状突起の3部からなる。

Wiki

The sternum or breastbone, in vertebrate anatomy, is a flat bone that lies in the middle front part of the rib cage. It isendochondral in origin.^[1] It probably first evolved in earlytetrapods as an extension of the pectoral girdle; it is not found in fish. In amphibians and reptiles it is typically a shield-shaped structure, often composed entirely of cartilage. It is absent in both turtles and snakes. In birds it is a relatively large bone and typically bears an enormous projecting keel to which the flight muscles are attached.^[2] Only in mammals does the sternum take on the elongated, segmented form seen in humans. In some mammals, such as opossums, the individual segments (sternebrae) never fuse and remain separated by cartilagenous plates throughout life.^[2]

In arachnids, the sternum is the ventral (lower) portion of thecephalothorax. It consists of a single sclerite situated between the coxa, opposite thecarapace.

人間の肋骨は全部で二十四本で両側に十二本ずつ、それぞれ第一肋骨～第十二肋骨と名前が付いている。

そのうち第一肋骨～第七肋骨は胸骨外側縁と接しており完全に胸部を覆っているのに対して、第八肋骨～第十二肋骨は胸骨と接しておらず前腹部は開いている。肋骨全体としては肺と心臓をその内部に抱え、肝臓がその内部にほぼ収まる。

また肋骨は骨折しやすい骨としても知られている。一本一本が細く衝撃に対して弱いためであり、主な原因としては外衝撃のほかに咳などによる疲労骨折が挙げられる。他方で折れてもダメージが少ない場合がある骨でもある。深く折れて内臓に刺されば命取りになりかねないが、一本軽く折れた程度の場合、互いに支え合っているのでさほどの苦痛はない。

Wiki

Humans have 24 ribs (12 pairs). The first seven sets of ribs, known as "true ribs" (costae verae), are directly attached to the sternum through the costal cartilage. Rib 1 is unique and harder to distinguish than other ribs. It is a short, flat, C-shaped bone. The vertebral attachment can be found just below the neck and the majority of this bone can be found above the level of the clavicle. Ribs 2 through 7 have a more traditional appearance.^[1] The following five sets are known as "false ribs" (costae spuriae), three of these sharing a common cartilaginous connection to the sternum, while the last two (eleventh and twelfth ribs) are termed floating ribs (costae fluctuantes) or vertebral ribs. They are attached to the vertebrae only, and not to the sternum or cartilage coming off of the sternum. Some people lack one of the two pairs of floating ribs, while others have a third pair.

In general, human ribs increase in length from ribs 1 through 7 and decrease in length again through rib 12. Along with this change in size, the ribs become progressively oblique (slanted) from ribs 1 through 9, then less slanted through rib 12.^[1]