The development of the human body; a manual of human embryology . smay entirely fail, the result being the formation of only one-half of the body of the vertebra. Other anomalies result fromthe excessive development of parts. Thus, the rib of theseventh cervical vertebra may sometimes remain distinct andbe long enough to reach the sternum, and the first lumbar ribmay also fail to unite with its vertebra. On the other hand,the first rib is occasionally found to be imperfect. The Development of the Sternum.—The longitudinalbars which are formed by the fusion of the ventral ends ofthe anterior ei
The development of the human body; a manual of human embryology . smay entirely fail, the result being the formation of only one-half of the body of the vertebra. Other anomalies result fromthe excessive development of parts. Thus, the rib of theseventh cervical vertebra may sometimes remain distinct andbe long enough to reach the sternum, and the first lumbar ribmay also fail to unite with its vertebra. On the other hand,the first rib is occasionally found to be imperfect. The Development of the Sternum.—The longitudinalbars which are formed by the fusion of the ventral ends ofthe anterior eight or nine cartilaginous ribs represent the THE STERNUM. I89 future sternum. At an early period the two bars comeinto contact anteriorly and fuse together (Fig. 96), and atthis anterior end two usually indistinctly separated massesof cartilage are to be observed at the vicinity of the pointswhere the ventral ends of the cartilaginous clavicles artic-ulate. These are the episternal cartilages (em), whichlater normally unite with the longitudinal bars and form. Fig. 96.—Formation op the Sternum in an Embryo op about 3 , Clavicle; em, episternal cartilages.—(Ruge.) part of the manubrium sterni, though occasionally theypersist and ossify to form the ossa suprastemalia. Thefusion of the longitudinal bars gradually extends back-ward until a single elongated plate of cartilage results,with which the seven anterior ribs are united, one or twoof the more posterior ribs which originally took part in theformation of each bar having separated. The portions of 190 THE DEVELOPMENT OF THE HUMAN BODY. the bars formed by these posterior ribs constitute the ensi-form process. The ossification of the sternum (Fig. 97) partakes to acertain extent of the original bilateral segmental origin ofthe cartilage, but a marked condensation of the centers ofossification also occurs. In the portion of the cartilagewhich lies below the junction of the third costal cartilagesa series of pairs of ce
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectembryol, bookyear1902
