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

  • Charles Barrett Lockwood
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.

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    four or five of a series of longitudinal sections. Its closure is assisted by the growth of the mesoblast round the trachea and oesophagus, and seems to be effected in the same manner in the Human embryo as in the Rabbit, as may be seen by comparing the accompanying drawing of a transverse section of an early Human embryo with those of the Rabbit (fig. 46, It. V.). In rare instances th© iter venosum may persist, and I have seen in a Human foetus an aperture at the inner side of the vena cava superior which opened from the pericardial into the pleural sac ; this patency was associated with a tri-coelian heart and other abnormalities. The closure of the passage which I liave ventured to call the “ iter venosum ” is a matter of dispute. His, writing in 1881,'“ attributes the closure in Rabbits and Man mainly to the approximation of the Cuvierian ducts, I myself had arrived at a similar conclusion before having seen His’s paper. UsKOwt mentions three main factors in the occlusion. 1. The general alteration in the position of the foremost part of the mesocardium laterale. 2. A thickening of the “ massa longitudinalis ” (a name which the author gives to the tissues along the side of the trachea and oesophagus). 3. A cell increase in the “massa tra ns versa ” {i.e., the dorsal part of the diaphrag- matic mesoblast). This author also mentions the ducts of Cuvier in this connexion, but does not, in my opinion, attach sufficient importance to the part they play. The names “massa transversa” and “massa longitudinalis,” which Uskow uses, seem to me superfluous. Whilst the iter venosum is being occluded the lungs protrude from the oesophagus into the recessus abdominalis, and soon afterwards a septum, the dorsal pericardium, J originates betwixt them and the heart. The development of the dorsal pericardium is preceded by changes in the cardiac endings of the great veins, due to a gradual expansion of the sinus reuniens, and therefore these changes may be mentioned before the septum. The sinus, as we have seen, is formed from the cardiac ends of the vitelline veins, and retains for a time the features of those vessels, and is situated at the dorsal edge of the primitive splanchnic retroflexion, or septum transversum. By the time the jugular veins have appeared the sinus reuniens has expanded and become more capacious, but it does not at first receive those vessels, for, as we have seen, they open into the ends of the umbilical veins (fig. 6, A. C. V.). As the expansion of the sinus reuniens proceeds it involves the mouths of the umbilical veins, and they are gradually merged into, and become part of, the sinus (fig. 36, S. R. and L. U. V., also figs. 33e and 38f and 39f, R. U. V. and S'. R.) ; and at last it progresses so firr that the jugular veins (or ductus Cuvieri) acquire separate openings of their own (figs. 37f, 38f, S'. R. and R., and L. C. D.). Thus, by the time the lungs and pericardium have begun (eleventh day), the sinus reuniens receives on either side three great veins, * “ Mittheilungen znr Emb. der Saugetbiere, &o.,” ‘ Arch, fiir Anat. und Pbys.,’ 1881, p. 318. t Ihid., p. 174. t Called by some authors, Schmidt, His, and Uskow, memhrana pleuro^pericardiaca.
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