The development of the human body; a manual of human embryology . T 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 centers appears just about birth, eachcenter probably representing anepiphysial center of a correspond-ing rib. Later the center
The development of the human body; a manual of human embryology . T 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 centers appears just about birth, eachcenter probably representing anepiphysial center of a correspond-ing rib. Later the centers of eachpair fuse and the single centers soformed, extending through thecartilage, eventually unite to formthe greater part of the each of the two uppermost seg-ments, however, but a singlecenter appears, that of the lowersegment uniting with the moreposterior centers and forming theupper part of the gladiolus, whilethe uppermost center gives rise tothe manubrium, which frequentlypersists as a distinct bone united tothe gladiolus by a Fig. 97.—Sternum ofNew-born Child,showing Centers ofOssification. / to VII, Costal cartilages.—(Gegenbaur.) A failure of the cartilaginous barsto fuse produces the condition knownas cleft sternum, or if the failure to fuse affects only a por-tion of the bars there results a perforated sternum. A per-foration or notching of the ensiform cartilage is of frequentoccurrence owing to this being the region where the fusionof the bars takes place last. The suprasternal bones are the rudiments of a large bone,the episternum, situated in front of the manubrium in thelowest mammalia and reptilia. It furnishes the articular sur-faces for the clavicles and is possibly formed by a fusion of the THE I9I ventral ends of the cartilages which represent those bones,hence its appearance as a pair of bones in the rudimentarycondition. The Development of the Skull.—Little is as yet known,especially in the human embryo, concern
Size: 1121px × 2229px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, booksubjectembryol, bookyear1902
