Page:Encyclopædia Britannica, Ninth Edition, v. 1.djvu/864

Rh 820 A N A T O M Y [SKELETON not only by peculiarities in form, appearance, and structure, but by possessing special functions and uses. Thus the bones collectively form the Osseous system; the joints the Articulatory system; the muscles, which move the bones at the joints, the Muscular system; and these several systems collectively constitute the organs of Locomotion. The blood and lymph vessels form the Vascular system ; the brain, spinal marrow, and nerves, the Nervous system, with which is intimately associated the organs of Sense ; the lungs and windpipe, the Respiratory system; the alimentary canal, with the glands opening into it, the Digestive system; the kidneys, bladder, and urethra, the Urinary system ; the testicles, spermatic ducts, and penis in the male, with the ovaries, uterus, and clitoris in the female, the Generative or Reproductive system; the skin, with the hair and nails, the Tegumentary system. These various systems are so arranged with reference to each other as to form an organic whole. ANATOMY OP THE OEGANS OP LOCOMOTION. The organs of locomotion consist of the muscles or active organs, and the bones and joints or passive organs. The anatomy of the bones will first attract our attention. Skeleton. &quot; OSSEOUS SYSTEM OSTEOLOGY SKELETON. The WOl d Skeleton (from o-KeAAco, to dry] signifies literally the dry or hard parts of the body. When used in a limited sense it is applied merely to the bones, but when used in a wider and more philosophic sense it comprises not only the bones or osseous skeleton, but the cartilages and fibrous mem branes which complete the framework of the body. The first evidence of a skeleton in the embryo is the appear ance of membranes in many parts of which cartilage is developed, and in course of time this cartilage is converted into bone. In some animals, however, as in the cartila ginous fish, the osseous conversion does not take place, and the skeleton remains permanently cartilaginous; and in the very remarkable fish called Lancelot, or Amphioxus, the skeleton consists almost entirely of fibrous membrane. ^ The skeleton serves as a basis of support for the soft parts, as affording surfaces of attachment for muscles and as a protection for many delicate organs. In the verte- brata the osseous skeleton is clothed by the muscles and skin, and is technically called an endo-skeleton. In inverte- brata the skeleton is not unfrequently on the surface of the body, and is termed an exo- or dcrmo-slceleton. In some vertebrates (e.g., the armadillo, tortoise, and sturgeon), in addition to the proper endo-skeleton, skeletal plates are developed in connection with the integument, so that they possess a dermo-skeleton likewise. In some vertebrates, also, a partial skeleton is formed within the substance of some of the viscera e.g., in ruminant animals a bone is situated in the heart ; in the walrus and other carnivora, in rodents, bats, and some monkeys, a bone lies in the penis; and in the leopard, jackal, and other carnivora, a cartilaginous style lies in the middle of the tongue. These parts form a tylanchno- or visceral skeleton. By some anatomists the teeth, which are unquestionably hard parts of the body, are also referred to the splanchno-skeleton, though they are special modifications of the papillae of the mucous membrane of the gum. In man, the teeth being excluded, there is neither exo- nor splanchno-skeleton, but only an endo-skeleton. In each of the great subdivisions of the body an endo- skeleton exists, so that we may speak of an Axial Skeleton and an Appendicular Skeleton. The Axial Skeleton con sists of the bones of the spine and head, the ribs, and the breastbone; the Appendicular Skeleton, of the bones of the limbs. The number of bones in the skeleton varies at different periods of life. In the adult there are about 200, but in the child they are more numeroiis ; for in the pro cess of consolidation of the skeleton certain bones originally distinct become fused together. In Plates XII., XIII., and XIV., front, back, and side views of the entire skeleton are given, together with figures of the skull and several of its constituent bones. We shall commence the description of the AXIAL SKELE TON by giving an account of the bones of the spine. The SPINE, SPINAL or VERTEBRAL COLUMN, chine, or back- Spine, bone, consists of a number of superimposed bones which are named Vertebrae, because they can move or turn some what on each other. It lies in the middle of the back of the neck and trunk ; has the cranium at its summit ; the ribs at its sides, which in their turn support the upper limbs; whilst the pelvis, with the lower limbs, is jointed to its lower end. The spine consists in an adult of twenty- six bones, in a yoitng child of thirty-three, certain of the bones in the spine of the child becoming ankylosed or blended with each other in the adult. These blended bones lose their mobility, and are called false vertebras ; whilst those which retain their mobility are the true vertebra?. In the vertebrata the bones of the spine are arranged in groups, which may be named from their position vertebrae of the neck or cervical; of the chest, dorsal or thoracic ; of the loins, lumbar ; of the pelvis, FlG 5 _ The AxJ *, Skcleton sacral; and of the tail, coccy- geal or caudal ; and the num ber of vertebrae in each group maybe expressed in a formula. In man the formula is as fol lows: C 7 Di2L 5 S 5 Coc4 = 33 bones, as seen in the child; but the five sacral vertebrae fuse together into a single bone the sacrum and the four coccygeal into the single coccyx. Hence the sacrum and coccyx of the adult are the false, whilst the lumbar, dorsal, and cervical are the true vertebrae. The vertebrae are irregularly-shaped bones, but as a rule have certain characters in common. Each possesses a body and an arch, which enclose a ring, with certain pro cesses and notches. The Body, or Centrum, is a short cylinder, which by its upper and lower surfaces is con nected by means of fibro-cartilage with the bodies of the vertebrae immediately above and below. The collective series of vertebral bodies forms the great column of the spine. The Arch, also called Neural Arch, because it en closes the spinal marrow or nervous axis, springs from the back of the body, and consists of two symmetrical halves united behind in the middle line. Each half consists of an anterior part or pedicle, and a posterior part or lamina. The Rings collectively form the spinal canal. The Pro cesses usually spring from the arch. The spinous process projects backwards from the junction of the two laminae, and the collective series of these processes gives to the entire column the spiny character from which has arisen the C0C4 C 7. tha cervical vertebra; r&amp;gt; 12, the dorsal; L 5j the lumbar; S 5, the sacral; Coc 4 , the coccygeal; CC, the series of twelve ribs on one side ; Ps, the pne-sternum ; Ms, the mcso-sternnm ; Xs, the xiphl- sternum. The dotted line VV repre sents the vertical axis of the spine.