. Human embryology and morphology. Embryology, Human; Morphology. 286 HUMAN EMBRYOLOGY AND MORPHOLOGY. six or more sternebrae being then present. In man the number has been reduced to seven pairs, the sternal ends of the seventh pair lying in front of the base of the ensiform process. It is not uncommon to find the 8 th rib reaching the sternum, especially on the right side; it is rare to find the 7th pair fail to reach the sternum. The more frequent presence of an 8 th sternal rib on the right side is due to right-handedness (Cunningham) or the pressure of the underlying liver requiring suppo
. Human embryology and morphology. Embryology, Human; Morphology. 286 HUMAN EMBRYOLOGY AND MORPHOLOGY. six or more sternebrae being then present. In man the number has been reduced to seven pairs, the sternal ends of the seventh pair lying in front of the base of the ensiform process. It is not uncommon to find the 8 th rib reaching the sternum, especially on the right side; it is rare to find the 7th pair fail to reach the sternum. The more frequent presence of an 8 th sternal rib on the right side is due to right-handedness (Cunningham) or the pressure of the underlying liver requiring support (Tredgold). Development of the Sternum.—The sternum is developed in the mesoblast of the ventral median line between the first 8 or 9 dorsal segments (Paterson). It is developed in two parts—a right from the right somatopleure, a left from the left somato- pleure. These two halves, the right and left fibrous sternal bars, fuse gradually in the middle line, the process of fusion commencing at the presternum and spreading back (Fig. 232). The bifurcated end of the ensiform process represents the posterior extremities of the sternal bars. epi coracoid element basis of clavicle ;~S$k:^^^lis^-2nd rib (chondrified). r-^centres of chondrification sternal bar ventral median line Fio. 232.—The Sternal Bars in a human embryo of six weeks (after Paterson). The sternum is described here as a structure arising in- dependently in the median ventral line. This, however, is not the commonly accepted view. Euge's researches led him to the conclusion that the segments of the sternal bars were produced as. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Keith, Arthur, Sir, 1866-1955. London : E. Arnold
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectembryol, bookyear1902
