Archive image from page 137 of Cunningham's Text-book of anatomy (1914). Cunningham's Text-book of anatomy cunninghamstextb00cunn Year: 1914 ( 104 OSTEOLOGY. or seven cartilaginous ribs. Paterson, on the other hand, regards the sternum as arising independently of the ribs by the union of a right and left sternal bar in the median ventral hue. There are also reasons for supposing that the presternum is intimately associated with the development of the ventral part of the shoulder girdle. Ossification of the Vertebrae.—The vertebrae are developed by ossification of the cartilage which surrounds
Archive image from page 137 of Cunningham's Text-book of anatomy (1914). Cunningham's Text-book of anatomy cunninghamstextb00cunn Year: 1914 ( 104 OSTEOLOGY. or seven cartilaginous ribs. Paterson, on the other hand, regards the sternum as arising independently of the ribs by the union of a right and left sternal bar in the median ventral hue. There are also reasons for supposing that the presternum is intimately associated with the development of the ventral part of the shoulder girdle. Ossification of the Vertebrae.—The vertebrae are developed by ossification of the cartilage which surrounds the notochord and which passes dorsally over the sides of the vertebral canal. The centres for the bodies first appear in the lower thoracic vertebras about the tenth week. An oval nucleus develops in each body. At first it is placed dorsal to the notochord, but subsequently surrounds and causes the disappearance of that structure. Occasionally, however, the primitive centre appears to be formed by the coalescence of two primary nuclei. Support is given to this view by the occasional occurrence of vertebrae in which the body is developed in two lateral halves, or in cases where only one-half of the body persists (Turner); normally, however, it is impossible to make out this division. From these single nuclei the bodies are developed, the process extending up and down the column until, by the fifth month, all the centra possess ossific nodules, except the coccygeal segments. About the seventh week a single centre appears in the vertebral arch on either side. These commence first to ossify in the upper cervical region and extend rapidly downwards throughout the column. They first appear near the bases of the superior articular processes, and extend backwards into the laminae, laterally into the transverse processes, and forwards into the roots of the vertebral arches. These latter project anteriorly and form a considerable portion of the postero-lateral aspects of the body, fr
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