. The dinosaurs of North America. Dinosaurs. MABSH.] 175 through the centra, a thin septum usually remaining. In the median caudals a deep cavity on each side exists, as shown in figs. 24-26, below. On the distal caudals the lateral cavity has nearly or quite disap- peared. All the caudal vertebrse are proportionally shorter than in Diplodocus, and their chevrons have no anterior projection, as in that genus. The remains on which the present description is based are from the Atlantosaurus beds of South Dakota, about 200 miles farther north than this well-marked horizon has hither
. The dinosaurs of North America. Dinosaurs. MABSH.] 175 through the centra, a thin septum usually remaining. In the median caudals a deep cavity on each side exists, as shown in figs. 24-26, below. On the distal caudals the lateral cavity has nearly or quite disap- peared. All the caudal vertebrse are proportionally shorter than in Diplodocus, and their chevrons have no anterior projection, as in that genus. The remains on which the present description is based are from the Atlantosaurus beds of South Dakota, about 200 miles farther north than this well-marked horizon has hitherto been Fig. 24.—Candal vertebra of Barosaurus lentus Marsh; side view. Fig. 25.—The same vertebra, in section j front view. Fir,. 26.—The same vertebra; bottom view. All the figures are one-eighth natural size. a. anterior end; c, face for chevron; /, lateral cavity; p. posterior end; *. section. DIPLODOCIDJE. THE SKULL. The skull of Diplodocus is of moderate size. The posterior region is elevated and narrow. The facial portion is elongate and the anterior part expanded transversely. The nasal opening is at the apex of the cranium, which from this point slopes backward to the occiput. In front of this aperture the elongated face slopes gradually downward to the end of the muzzle, as represented in PI. XXV, fig. 1. Seen from the side the skull of Diplodocus shows five openings: a small oval aperture in front, a large antorbital vacuity, the nasal aper- ture, the orbit, and the lower temporal opening. The first of these has not been seen in any other Sauropoda; the large antorbital vacuity is characteristic of the Theropoda also; while the other three openings are present in all the known Dinosauria. On the median line, directly over the cerebral cavity of the brain, the type specimen of Diplodocus has also a fontanelle in the parietals. This, however, may be merely an individual peculiarity. The plane of the occiput is of moderate size, and form
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