Paper - Vertebral Regional Determination in Young Human Embryos
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Bardeen CR. Vertebral regional determination in young human embryos. (1908) Amer. J Anat. 2: 99 - 105.
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Vertebral Regional Determination in Young Human Embryos
From - Abstracts of some of the papers read at the meeting of the association of American anatomists, Chicago, January 1, 2 and 3, 1908
By Charles Russell Bardeen, University of Wisconsin.
In 1904 I published a study of numerical vertebral variation in the human adult and embryo (Anat. Anz., XXV. p. 498). In this article I took exception to the views advanced by Rosenberg in 1876 (Morph. J ahrb.) that in young human embryos the sacrum is composed of a more distal set of vertebrae than it is in the adult, and that during embryonic development there is a reduction in the number of thoracic or rib-bearing vertebrae.
Rosenberg has recently (Morph. Jahrb., XXXVI, p. 609, 1907) criticised my paper on two grounds:
- That some of the data used in the statistical tables are incorrect, inaccurate or without suﬂicient basis.
- That the data used are incorrectly interpreted.
In support of the first criticism that data used in the table are inaccurate or inadequate, Rosenberg goes into a careful study of the embryos tabulated from his article of 1876 and of the embryos described by Hagen and by Peterson. He finds only two of his embryos correctly described by me and that the embryos of Hagen and Peterson are not described by these authors with suﬂicient detail to merit their inclusion in a statistical table.
Neither Rosenberg nor the other authors mentioned gave specific detailed accounts of the vertebral columns of the embryos studied. Rosenberg took up each of the regions of the vertebral column in turn and used various embryos to illustrate each region. The data concerning each embryo had to be gathered from the somewhat involved account which he gave concerning the different regions of the spinal column and from his figures. In deducing that Rosenberg’s Embryo V‘ had a “normal” vertebral column I undoubtedly, as Rosenberg says in his recent article, had no sufficient data. The other inaccuracies which he attributes to me are due rather to interpretation from a point of view different from that of Rosenberg than to a mistake concerning the data which be furnished. It was, however, a mistake to attribute 5 instead of 6 coccygeal vertebrae to Embryos IV’ and III‘.
In utilizing the somewhat incomplete data of Hagen and Peterson I probably should have called more attention to the incompleteness of these data. Lack of better material led to their inclusion in the table.
The chief difference between the views maintained by Rosenberg and those which I have advanced comes from the interpretation which we give to embryonic data. Rosenberg would apply to embryos the ordinary criteria which are applied to the adult osseous skeleton in determining the cervico-thoracic, thoraco-lumbar, lumbo-sacral, and sacro-coccygeal boundaries, while to me it seems evident that the special features characteristic of the embryo must be taken into account. Rosenberg thinks that it is incorrect to call a vertebra a lumbar vertebra unless its cartilaginous or osseous costal element is intimately fused with the transverse process, and that it is incorrect to call a vertebra a sacral vertebra unless its cartilaginous or osseous costal element is intimately fused laterally into the lateral sacral plate. Thus, likewise, a vertebra is not a true cervical vertebra unless its costal element is intimately fused with the transverse process.
My studies of the development of the vertebral column have led me to the conclusion that there are separate centers of chondrification for the costal elements of each of the vertebra, from the first cervical to, and sometimes possibly including, the first coccygeal. In connection with the more distal coccygeal vertebra apparently no cartilaginous costal elements develop. I do not, however, agree with Rosenberg that progressive ontogenetic regional alteration is to be deduced from the independent origin of cartilaginous costal elements in connection with vertebra: to which these elements are firmly fused in the adult.
Let us take up brieﬂy the development of the costal elements in the vertebrae in each of the regions of the spinal column.
1. Cervical Region
The cervical region becomes distinct. from the thoracic in the fifth week, at a period when centers of chondrification in the vertebrae are about to appear. The two regions are rendered distinct from one another by the rapid extension of the blastemal costal processes of the thoracic vertebrae into the thoracic wall (fig. 1B). Th blastmal processes of the seventh cervical vertebra extend outwards further than those of the other cervical vertebrae, but there is less difference in length between the costal processes of the seventh cervical vertebra and those of the other cervical vertebrae than between those of the seventh cervical vertebra and those of the first thoracic. The great difference in length between the costal processes of the seventh cervical vertebra and those of the first thoracic is clearly indicated in the figures of Charlotte Muller. (Morph. J ahrb., 1906.)
Fig. 1B. Diagram of the skeleton of an embryo 11 mm. long and about five weeks old.
0, occipital plate. 1'. first lumbar vertebra. c, ﬂrst cervical vertebra. 3', first sacral vertebra. t’, that thoracic vertebra. co’, first coccygeal vertebra.
In the costal process of the seventh cervical vertebra a center of chondrification is formed at the period when similar centers appear in the ribs. For this reason it may be correct to speak of the regular appearance of a pair of cartilaginous cervical ribs. I believe, however, that it would be more correct to speak of the costal elements of the seventh cervical vertebra as being more rib-like than those of the other cervical vertebrae rather than as true ribs. Normally they do not extend much beyond the transverse processes. The centers of chondrification for the costal elements of the other cervical vertebrae appear much later than those of the seventh cervical vertebra (usually not until the embryo has reached a length of from 16-18 mm.), and they fuse earlier with the transverse processes.
During the period of ossification, according to Leboucq, 1896, the ventral limb of the transverse process in most of the cervical vertebrae is ossified by ingrowth at one end from the pedicle, at the other from the tip of the transverse process. In the seventh cervical vertebra frequently, in the sixth occasionally, and in the fifth, second and fourth rarely, there arise during the second "to the fifth months separate centers of ossification for the costal elements. According to Mall (Am. Journ. Anat., 1906), it is not certain that separate centers of ossification for the costal elements of the seventh cervical vertebra in the embryo are very much more frequent than cervical ribs in the adult. Undoubtedly cervical ribs are more common than one is led to believe from statistical studies of vertebral variation.
The presence of a more or less rib-like costal element in young human embryos would doubtless make it difficult or impossible to compare the relative frequency of “cervical ribs” in the adult and embryo. It would not be easy to determine how great a development of the costal element in the embryo would be necessary in order to make it comparable with a free cervical rib in the adult.
2. Lumbar Region
This region becomes clearly marked off from the thoracic in the fifth week of embryonic development by the rapid growth which takes place at this time in the blastemal costal processes of the thoracic vertebrae. ( See fig. 1B.) This is shown not only in the embryos which I have studied, but also in those figured by Charlotte Muller, 1906. Slightly, later it becomes distinguishable from the sacral region by fusion of the blastemal cartilaginous costal processes of the latter to form a. lateral sacral plate, the proximal part of which becomes united to the blastemal ilium (Bardeen, Am. Journ. Anat., 1905, figs. 5 and 6). In the lumbar vertebrae it seems probable that there are separate centers of chondrification for each of the metal elements. These appear later than the centers for the ribs in the thoracic region and they very quickly fuse with the cartilaginous transverse processes. Usually they bear no close resemblance to the true ribs (see figures by Charlotte Muller, 1906). The centers for the costal elements of the first one or two lumbar vertebrae may appear a little earlier and fuse a little later with the transverse -processes than those of the other lumbar vertebrae, but they are not, it seems to me, to be classed as ribs and the vertebrae to which they belong classed as thoracic or thoraco-lumbar, unless they bear so strong a morphological resemblance to the ribs as to seem to come in series with these. This normally is not the case. There is usually a sharp change of form from the twelfth thoracic rib to t11e costal element of the first lumbar vertebra. As a rule there are no separate centers of ossification for the costal elements of the lumbar vertebrae. In twenty embryos less than one hundred days old studied by Mall (American Journal of Anatomy, 1906), in which the other ribs were present, there were no centers of ossification for the twelfth rib in eight instances. In no instance was there a separate center of ossification for a thirteenth (first lumbar) rib. In two instances there were separate centers of ossification for a cervical rib.
Fig. 1A. Diagram of the vertebral column of an embryo 7.5 mm long and about four weeks old.
0, occipital plate. t’, first thoracic scleromere. c, first occipital scleromere. s‘, first sacral scleromere. 1‘, first lumbar scleromere.
There is, it seems to me, no evidence of an ontogenetic reduction of the distal portion of the thoracic region.
This region becomes distinct during the sixth week owing to the fusion of the distal ends of the blastemal costal processes to form a lateral sacral plate. Separate chondrogenous centers for the costal elements frequently, if not constantly, arise, but they quickly fuse at he base with the cartilaginous transverse processes of the neural arches. Laterally the cartilaginous costal processes become united to one another within the blastemal lateral sacral plate. The processes of the first three sacral vertebra usually become thus united before the third is joined by the fourth and the fourth by the fifth. Judging from Rosenberg’s studies, the processes of the second and third vertebrae frequently become united before being joined by those of the first sacral vertebra, but this is by no means constantly the case. I do not agree with Rosenberg that the first sacral vertebra must be called a lumbo-sacral vertebra. until the ends of its cartilaginous costal transverse processes are intimately fused with those of the second sacral vertebra. In early embryonic development the surrounding blastema must be taken into account.
These first become distinct from the sacral vertebrae during the latter part of the sixth week, when the ends of the costal elements of the acral vertebra become united by blastemal tissue. It is, however, by no means always easy to distinguish the sacro-coccygeal boundary at this period because the transverso-costal elements of the first coccygeal vertebrae are relatively well developed and may become united by strands of connective tissue with those of the last sacral. The thirtieth vertebrae at this period should not, however, be counted as an integral part of the sacrum unless the costal elements really help to form the lateral sacral plate. When cartilage unites the ends of the costal elements of the sacral vertebrae into a cartilaginous lateral sacral plate it becomes easy to distinguish the sacral from the coccygeal vertebrae. If the costal elements of the thirtieth vertebra are united by cartilage to the twenty-ninth it becomes a sacral vertebra, but not otherwise. This condition is not infrequent in embryos, but it must be remembered that sacra with six vertebrae are frequently found in the adult. It is uncertain whether or not the costal element of the first coccygeal vertebra normally has a separate center of chondrification. It is fairly certain that no such centers are found in the other vertebrae.
During the period of ossification separate centers usually appear for the costal elements of each of the first three sacral vertebrae. It is said that these centers may appear merely in the first two vertebrae. They may appear in all five.
In conclusion, I may say, it seems to me, that the data at present available go to show that regional variation in the embryonic vertebral column corresponds approximately with that in the adult. A study of a large number of embryos correlated with a study of vertebral variation in the race from which the embryos came is necessary before accurate data on the subject can be obtained.
Cite this page: Hill, M.A. (2020, July 4) Embryology Paper - Vertebral Regional Determination in Young Human Embryos. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Paper_-_Vertebral_Regional_Determination_in_Young_Human_Embryos
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