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

Date:
1892
Catalogue details

Licence: Public Domain Mark

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

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    I 39. The thoracic cavities have for a time the form of tubular spaces lying on the dorsal side of the heart and on either side of the spinal column J they receive the developing lungs, and still communicate caudad with the abdominal cavity. 40. The two thoracic cavities are separated from the abdominal cavity by the fusion of the dorsal rim of the septum transversum with peritoneal folds of the dorsal wall of the trunk (the pillars of USKOW). 41. The diaphragm is composed of two parts, the ventral septum transversum, and a dorsal part, the pillars. 42. Upon its first establishment the liver grows into the septum transversum, but subsequently detaches itself from the latter and remains united to the diaphragm by means of its peritoneal covering only, the coronal ligament. II. The Development of the Skeleton. With the exception of the chorda dorsalis, which takes its origin from the inner germ-layer, the skeleton of Vertebrates is a product of the intermediate layer, resulting from a series of histological differentiations, a general survey of which has already (p. 540) been given. There have appeared many articles treating on this very complicated apparatus in the higher Vertebrates from a develop- mental and also especially from a comparative-anatomical standpoint. By an exhaustive treatment of this subject this part of the work would attain to greater proportions than the plan of the present text- book permits. I shall therefore limit myself to the more important concUtions of organisation and for what remains refer to the text- books of comparative anatomy. Two chief parts are distinguishable in the skeleton of Vertebrates : (1) the axial skeleton, which is in turn divisible into that of the trunk and that of the head, and (2) the skeleton of the limbs. The formei is the older and more primitive, being possessed by all Vertebrates; the latter has been developed later, and is entirely wanting in the lower groups (Amphioxus, Cyclostomes). A. The Development of the Axial Skeleton. The original foundation of the axial skeleton of all Vertebrates is the notochord or chorda dorsalis. By this is understood a flexible, rod-like structure, which is situated in the axis of the body 38