The early development of the pericardium, diaphragm, and great veins / by C.B. Lockwood.

  • Lockwood, Charles Barrett, 1856-1914.
Date:
1888
Catalogue details

Licence: Public Domain Mark

Credit: The early development of the pericardium, diaphragm, and great veins / by C.B. Lockwood. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

    16/40 (page 378)
    In the higher Mammals the diaphragm usually consists of three parts—^namely, of a central part, in relation with the pericardium and heart; of lateral parts, which are muscular ; and of crura. So far I have only traced the origin of the centi-al part, that which is interposed between the heart and liver. This is at first a thin layer of mesoblast, whose cells are arranged transversely (figs. 42f and 43f, also figs. 53 and 54h, S. 2\ or V. D). In many animals, e.g., the Dog, Rabbit, and Man, it splits towards the end of intra-uterine life into two distinct layers—a superior, which helps to form the pericardium ; and an inferior, which usually becomes tendinous, and is the tendinous centre of Human anatomists. In Man the fibrous pericardium and tendinous centre reunite after the third year, but they remain permanently apart in many Mammals, the azygos lobe being interposed between them. During the time that the Human peri- cardium is separable from the diaphragm it invests the thoracic part of the vena cava inferior with both its fibrous and serous layers, and these investments never entirely disappear. Further, although the liver also disassociates itself very widely from the central part of the diaphragm (figs. 63j and 64j), yet it always retains part of its original connexions by means of the lateral, coronary, and falciform ligaments. These are so arranged in most of the higher Mammals that they bisect each leaflet of the tendinous centre, and do not as a rule pass beyond their limits. The coronary ligament is complicated by the caval junction and by the development of the remaining portion of the diaphragm, the dorsal diaphragm, which will be described presently. The sides of the diaphragm begin to develop at the same time as the lungs, and increase as the thoracic region expands. They begin as a constriction between the liver and the body wall (fig. 43f, L.D.), and this constricted part gradually becomes longer (figs. 51g and 60i, L.D.), and is finally converted, in a greater or less degree, into muscular tissue. When the iter venosum of the Rabbit or of the Human embryo is just on the point of closure, a mesoblastic process, the dorsal diaphragm (UsKOw), grows from the body wall across the recessus pulmonalis, and ultimately partitions it from the hinder part of the pleuro-peritoneal cavity and thus completes the diaphragm. The ingrowth is the same on either side, and originates far forwards, close to the Cuvierian ducts. When it is first discernible the lungs are simple diverticula from the sides of the oesophagus (figs. 49g and 55h, Lng.). During its early stages the dorsal diaphragm has hardly any of the characters it ultimately attains, and, therefore, it is desirable to consider it at a stage at which its identity is not doubtful, and, yet, at which it has not lost its earlier peculiarities. The accompanying figure was made from a coronal section through a Rabbit’s embryo of the early part of the fourteenth day (fig. 35, D.D.). It would have been better, perhaps, had the specimen been a little less advanced; but, nevertheless, it suffices to exemj^lify the point I wish to make clear, namely, that the lateral attach- ments of the dorsal diaphragm to the side body wall are nearer the head than its median connexions. At this period, the fourteenth day, the various organs are well grown.