Text-book of the embryology of man and mammals / by Oscar Hertwig ; translated from the 3rd German edition by Edward L. Mark.

  • Oscar Hertwig
Date:
1899
Catalogue details

Licence: Public Domain Mark

Credit: Text-book of the embryology of man and mammals / by Oscar Hertwig ; translated from the 3rd German edition by Edward L. Mark. Source: Wellcome Collection.

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    that the axial skeleton undergoes a Segmentation into separate like portions, whicli are situated one behind another; to accomplish this, remnants of the parental tissue do not chondrify, bat become, between the bodies o£ the vertebra, the intervertebral discs, and, between the arches, the iigamenta intercruralia, etc. 10. The Segmentation of the vertebral column has been dependent in its origin upon the Segmentation of the musculature, and has -been effected in such a way that skeletal segments and muscular Segments alternate with one another, and that the longitudinal muscle-fibres, which lie alongside the axial skeleton, are attached by their anterior and posterior ends to two [adjacent] vertebra and are capable of moving them upon each other. 11. The chorda is more or less restrained in its growth by the cartilaginous bodies of the vertebra surrounding it, and degenerates in different ways in the different classes of Vertebrales ; in MammaLs the part located in the body of the vertebra is completely obliterated, whereas a remnant of it is preserved between vertebra and becomes the jelly-core of the intervertebral disc. 12. The cartilaginous vertebral column is converted in most Vertebrates into a bony one, by the breaking down of the carti- laginous tissue, which begins at different places, and its replacement by bony tissue. (Formation of bone-nuclei or centres of ossification.) 13. The ossification of each cartilaginous vertebral fundament in Mammals and Man proceeds from tkree centres, from one in the body and one in each half of the arcb, to which subsequently certain accessory centres are added. 14. With each vertebral segment there is associated a pair of ribs, which arise by a process of chondrification in the layei’s of tissue which separate the muscle-segments (the Iigamenta intermuscularis). 15. In Man the various regions of the vertebral column are produced by metamorphosis of the vertebral and costal fundaments. (1) The thoracic part of the vertebral column (dorsal vertebra) is cliaracterised by the following peculiarities : the ribs attain to complete development; a part of them become expanded at their ventral ends, and united to form the two sternal bars, by the fusion of which the unp lired sternum is produced. (Fissura sterni, an arrested torma- tion.) (2) In the cervical and lumbar regions of the column the funda- ments of the ribs remain small, and fuse with outgrowtlis from the vertebra;—the transverse processes—to form