. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. Production of Motion and Locomotion 647 Origin. ing ends, and is surrounded by a connective tissue sheath which at the ends becomes continuous with tendons, that in turn merge into the periosteum ensheathing the bones, thus securing anchorage for the muscle. One end of the muscle, the punctum fixum, where it is attached to the most stationary part of the skeleton, is the origin. The other end, the punctum mobile, where it connects with the part of the skel
. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. Production of Motion and Locomotion 647 Origin. ing ends, and is surrounded by a connective tissue sheath which at the ends becomes continuous with tendons, that in turn merge into the periosteum ensheathing the bones, thus securing anchorage for the muscle. One end of the muscle, the punctum fixum, where it is attached to the most stationary part of the skeleton, is the origin. The other end, the punctum mobile, where it connects with the part of the skeleton which it moves, is the inser- tion. Upon the contraction of a muscle the inser- tion is always pulled towards the origin. There may be several insertions, as in the serratus mus- cles along the back, or there may be more than a single origin, for example, in the biceps there are two present, giving it the name "; Sometimes, as in the trapezius muscle, which moves the head and shoulder, the punctum fixum may become the punctum mobile, according to the movement to be effected. The wide range of variation in form (Fig. 580) is a necessary adaptation in the accom- plishment of different movements. The original form of embryonic muscles shows sheets of fibers, or myotomes, extending between partitions of con- nective tissues, similar to the arrangement of muscles on the sides of the body of a fish. Out of this primitive alignment modifications are initiated (1) by delamination, or splitting flatwise; (2) by splitting lengthwise; (3) by proximo-distal division; and (4) by various degrees of fusion. The shapes that muscles assume also exhibit a great variety. The word itself (musculus, little mouse) indicates an originally rather compact form that has undergone much adaptive streamlining in successfully accomplish- ing different movements. The muscles of the limbs are often fusiform, like the shape of a single smooth muscle cell, since this type is less bulky for
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Keywords: ., bookcentury1900, booksubjectanatomycomparative, booksubjectverte
