The development of the human body; a manual of human embryology . , until those ofopposite sides come into contact in the mid-ventral this is accomplished, however, a longitudinalsplitting of each myotome occurs, whereby there is sepa-rated off a dorsal portion which gives rise to a segment ofthe dorsal musculature of the trunk and is supplied by theramus dorsalis of its corresponding spinal nerve. In thelower vertebrates this separation of each of the trunkmyotomes into a dorsal and ventral portion is much moredistinct in the adult than it is in man, the two portionsbeing separate
The development of the human body; a manual of human embryology . , until those ofopposite sides come into contact in the mid-ventral this is accomplished, however, a longitudinalsplitting of each myotome occurs, whereby there is sepa-rated off a dorsal portion which gives rise to a segment ofthe dorsal musculature of the trunk and is supplied by theramus dorsalis of its corresponding spinal nerve. In thelower vertebrates this separation of each of the trunkmyotomes into a dorsal and ventral portion is much moredistinct in the adult than it is in man, the two portionsbeing separated by a horizontal plate of connective tissue THE TRUNK MUSCULATURE. 223 extending the entire length of the trunk and being at-tached by its inner edge to the transverse processes of thevertebrae, while peripherally it becomes continuous withthe connective tissue of the dermis along a line known asthe lateral line. In man the dorsal portion is also muchsmaller in proportion to the ventral portion than in thelower vertebrates. From this dorsal portion of the myo-. Fig. 113.—Embryo of 13 mm. showing the Formation ok the RectusMuscle.—(Mall.) tomes are derived the muscles belonging to the threedeepest layers of the dorsal musculature, the more super-ficial layers being composed of muscles belonging to thelimb system. Further longitudinal and tangential divi-sions and a fusion of successive myotomes bring about theconditions which obtain in the adult dorsal musculature. 224 THE DEVELOPMENT OF THE HUMAN BODY. While the myotomes are still some distance from themid-ventral line another longitudinal division affectstheir ventral edges (Fig. 113), portions being thus sepa-rated which later fuse more or less perfectly to form longi-tudinal bands of muscle, those of opposite sides beingbrought into apposition along the mid-ventral line by thecontinued growth ventrally of the myotomes. In thisway are formed the rectus and pyramidalis muscles of theabdomen and the depressors of the hyoid
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectembryol, bookyear1902
