. The animans and man; an elementary textbook of zoology and human physiology. ne of the arm. Thetwo large shoulder blades at the back, the scapulas, are heldin place merely by muscles attached to the ribs. At theirouter ends they also articulate with the humerus. The pec-toral girdle articulates with the axial skeleton through theclavicles only. This adjustment permits a wide range ofmotion to the arms. Structure of a long bone.—A bone in a prepared skeleton,or one picked up in the field after it has been exposed tothe weather for a long time, shows only the mineral matterof which it is compo
. The animans and man; an elementary textbook of zoology and human physiology. ne of the arm. Thetwo large shoulder blades at the back, the scapulas, are heldin place merely by muscles attached to the ribs. At theirouter ends they also articulate with the humerus. The pec-toral girdle articulates with the axial skeleton through theclavicles only. This adjustment permits a wide range ofmotion to the arms. Structure of a long bone.—A bone in a prepared skeleton,or one picked up in the field after it has been exposed tothe weather for a long time, shows only the mineral matterof which it is composed. It has lost all of its organic orliving material. A fresh bone, procured from the butcher,shows the features indicated in fig. 169. At each end isan enlargement or head, with certain protuberances for theattachment of muscles. The ends are capped with densewhite elastic tissue or cartilage (fig. 170 d). These are thesurfaces that articulate with other bones. The central shaft(fig. 169, x-z) is covered with a sheath of connective tissue, 334 THE ANIMALS AND MAN Tmj Tm. Cpl the periosteum, which is bone-forming material. Surfacesfor articulation with otherbones are smooth and coveredwith cartilage (Cpl,Tr and Cp). A bone, sawed through themiddle, as shown in fig. 170,exposes a dense layer of hardbone (b) enclosing, at theends, a spongy mass of bonetissue (c), the spaces of whichare filled with red red blood corpuscles areformed. The shaft enclosesa space filled with yellowmarrow (a). This is rich infat and gelatin. This struc-ture secures the maximumof strength for a given amountof bone material. In the ribs,or other flat bones, the entireouter wall is dense and hard,while the entire central partis made up of a spongy massof bone filled with red marrow. Chemical composition ofbone.—Bone is formed frommaterials taken into the bodywith the food, chiefly lime,salts (mineral matter) and FIG. 169. Right humerus seen fromin front. Cp, rounded surface ofupper extrem
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Keywords: ., bookcentury1900, bookd, booksubjectphysiology, booksubjectzoology
