The nature of the shoulder girdle and clavicular arch in Sauropterygia / by H.G. Seeley.
- Harry Govier Seeley
- Date:
- [1892]
Licence: Public Domain Mark
Credit: The nature of the shoulder girdle and clavicular arch in Sauropterygia / by H.G. Seeley. 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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![§ 2. The Clavicular Arcli. (i.) Since tlie clavicular arch was figured in PI. HawTcinsi (‘ Geol. Soc. Quart. Journ.,’ 1874, p. 444), v. Zittel has figured the clavicular bones iu PI. laticeps (‘ Handbuch der Paliiontologie,’ vol. 3, p. 489) ; but, while the clavicles are clearly shown, the interclavicle is named episternum. The most important evidence of this structure in Plesio- sauridse, however, is to be seen in Plesiosaurus arcuatus (‘ Brit. Assoc. Rep.,’ 1839, p. 7fi; and ‘Cat. Foss. Kept, and Amph.,’ Part II, p] 163), pi'eserved in the British Museum. From that specimen, No. 2028*, the character has been attributed to Thaumatosaurus (loc. cit., p. 159): “ Omosternum consisting of a large single plate, much ex- panded transversely, with a wide and shallow anterior notch.”t The anterior margin of the interclavicle in this specimen resembles in contour that attributed to Eretmosaurus (‘ Geol. Soc. Quart. Journ.,’ 1874s, p. 445) in its wide open curvature ; but there is no evidence to show whether the shoulder girdle, pelvis, and limbs in Plesiosaurus l arcuatus were constructed on the same plan as in PI. rugosus. There • \ is no doubt that the bone consists of three distinct elements united by ; sutures. These are a median interclavicle and two lateral bones j which I regard as clavicles. On the visceral aspect the triangular < clavicles are separated from each other by the wide short posterior J median bar of the interclavicle, but the clavicles extend forward so J that only a narrow transverse bar of the T-shaped interclavicle is exposed in front of them, extending across the entire width of thej| bone. The interclavicle is 10 j inches wide, concave on its anterior® margin, inch from front to back at the widened extremities of tlie cross-bar, and xSo inch in the same measurement towards the oblong : middle portion of the bone. The right anterior transverse limb of the cross-bar is 4 inches wide ; the left limb is 3 inches wide. The middle portion of the bone is 3£ inches wide and 2X inches in antero-Ij posterior measurement. The sutural line which defines the inter- clavicle is sagittal, and consequently irregular. On each side of this “[-shaped interclavicle (fig. 2), in contact with the posterior margin of its transverse bar and the lateral margin of its short wide median stem, is a large triangular clavicle which is directed backward and outward. In harmony with the dimensions of the transverse bar, the right clavicle is the wider. Anteriorly it is 4f inches wide; it is nearly 6 inches long. The external border, which is slightly convex, is con- tinuous with the truncated lateral termination of the interclavicle in front of it. These external margins diverge outward as they extend * backward, so that the transverse measurement over the posterior extremities of the clavicles is 14| inches. The postero-internal t Compare Sollas, ‘Geol. Soc. Quart. Journ.,’ vol. 37, 1881, p. 457.](https://iiif.wellcomecollection.org/image/b22412700_0014.jp2/full/800%2C/0/default.jpg)
