. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. The Skeleton S2- A diagram of such a movable joint (Fig. 424) shows that the two neigh- boring bones do not come into direct contact with each other, but instead their frictional surfaces are faced with yielding cartilage. Between these car- tilage surfaces there is inserted a closed sac, or bursa, filled with a lubricating synovial fluid continuously secreted by the cells lining the sac. Outside of these skeletal elements a fibrous air-tight sheath holds
. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. The Skeleton S2- A diagram of such a movable joint (Fig. 424) shows that the two neigh- boring bones do not come into direct contact with each other, but instead their frictional surfaces are faced with yielding cartilage. Between these car- tilage surfaces there is inserted a closed sac, or bursa, filled with a lubricating synovial fluid continuously secreted by the cells lining the sac. Outside of these skeletal elements a fibrous air-tight sheath holds the bones together by atmospheric pressure without muscular effort. In mountain climbing a familiar experience is a sense of heaviness at the joints, resulting from the change in atmospheric pressure. Outside of the joint there is an equipment of muscles controlled by directive nerves. Thus the operation of movable joints involves the combined action of bone, cartilage, connective tissue, muscle, and nerve. III. DIVISIONS OF THE SKELETON The hard skeletal parts are usually grouped into the axial and the appen- dicular divisions of the skeleton. The axial skeleton includes the skull, verte- bral column, ribs, and sternum, while the appendicular is composed of the pectoral and pelvic girdles as well as the skeleton of the appendages. Interdorsal \ Interventral \ \ \ Dorsal Spine Uorsa I \ \ ^IC i * Median Septum- /^T\~7"\, /, . s f~~7~/1 Notochorda! Sheath-.^!^^)))j>^ Dorsal Basidorsal / / Basiventral J-lorizontal "T" Septum Mesentery-Tr-f Intestine—r-^rrfj^ Ventral Rib -SL—lU Coelon. Coelomic Wall Ventral Median Septum""' ^-== Fig. 425. Diagram of the connective tissue system of the trunk of a vertebrate, showing relation of axial skeleton to transverse and longi- tudinal septa. Oblique view of left side. (After Goodrich.) As described in Chapter VII, the cartilaginous and bony elements are laid down first as connective tissue. During e
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