The limbs of the Brontotherida were intermediate in proportion between those of the Elephant and the Rhinoceros. The scapula is large, with a prominent spine and small coracoid process. The humerus is stout, and its great tuberosity extends above the head. The radial crest is prominent, and the entire distal end is occupied by the articulation. The olecranon cavity is shallow, and the condylar ridge similar to that of the Elephant, but not continued so far up the shaft. The radius and ulna are separate. The ulna has its olecranon portion much compressed. Its distal end is much smaller than in Rhinoceros, and has no articular face for the lunar. The radius is stout, and its distal end expanded. The carpal bones form interlocking series. They are shorter than in Rhinoceros, and support four well developed toes of nearly equal size. (Plate XIII, figure 2.) The metacarpal bones are shorter than those of Rhi noceros, the first phalanges longer, and the second series shorter. All the toes had "navicular" sesamoid bones, similar to that on the coronary bone of the horse. The ungual phalanges are short and tubercular, as in the Dinocerata and Proboscidea. The pelvis is much expanded transversely. The femur has a small third trochanter, and its head a deep pit for the round ligament. At the distal end, the anterior articular surface is narrow, and the two edges are of nearly equal prominence, as in the Tapir. The patella is elongate, and has a strong vertical keel on its articular face. The tibia is stout, and has a distinct spine. The fibula is separate and entire, but quite slender. The calcaneum is much elongated. The astragalus is shorter than in the Rhinoceros, and the superior groove more oblique. The cuboid face is larger than in Rhinoceros. The navicular has its distal facets subequal. There were three toes of nearly equal size in the pes, the first and fifth being entirely wanting. (Plate XII, figure 1.) None of the bones of the skeleton are hollow. There appear to be four well marked genera in the Brontotheridae, now known, which may be distinguished as follows: 1. Menodus Pomel.* (Titanotherium Leidy, 1852.) Diastema behind upper canines. Basal ridge on inner side of upper premolars not continuous. Nasals short. A postorbital process. Third trochanter rudimentary or wanting. Type M. Proutii. 2. Megacerops Leidy. (Megaceratops Cope), (Symborodon Cope in part.) Dentition = Incisors; canines; premolars ; molars 3 *Bib. Univ. de Genève, x, p. 75, Jan., 1849. 3 3 Diastema behind upper canines. Inner basal ridge on upper premolars not continuous. Nasals more elongated. A postorbital process. Third trochanter rudimentary or wanting. Type Megacerops Coloradensis Leidy. 3. Brontotherium Marsh, (Symborodon Cope, in part.) (Miobasileus Cope.) 2 1 4 3 Dentition =Incisors; canines; premolars; molars 3 No superior diastema. Strong continuous basal ridge on inner side of upper premolars. No postorbital process. Third trochanter distinct. Type B. gigas Marsh. 4. Diconodon Marsh (Anisacodon). 4 3 Dentition =Incisors; canines; premolars; molars- 3 No superior diastema. Strong inner basal ridge on upper premolars. Last upper molar with two inner cones. No postorital process. Type D. montanus Marsh. In the dentition and skeleton, the Brontotheride more nearly resemble the Eocene Diplacodon, than any other American genus, and they may yet prove to be nearly related. The animals of that genus were of much smaller size, and entirely without horns. The relations of the Brontotheride to the genus Chalicotherium Kaup, cannot at present be determined. In comparing the Brontotherida with the equally gigantic Dinocerata of the Eocene, several striking points of resemblance will be at once noticed; especially the presence of horn-cores in transverse pairs; the general structure of the limbs; and the short and thick toes. The differences, however, between these two groups are still more marked. In the Brontotherida there is but a single pair of horn-cores, and no crest around the vertex. The structure and number of the teeth are quite different, while the small canines and huge molars contrast strongly with the elongated canine tusks and diminutive molars of the Dinocerata. The latter, moreover, have two very large dependent processes on each ramus of the mandible; the cervical vertebræ flat; the femur without a third trochanter; and at least an additional toe in each foot. Among the features which this group shares with the Proboscidea may be mentioned: the superior extension of the condylar ridge of the humerus; the short thick toes; and the late union of the epiphyses with the centra of the vertebræ. The last character appears to belong especially to mammals of very large size, and probably indicates late maturity, and great longevity. The Brontotherida nearly equaled the Elephant in size, but the limbs were shorter. The nose was probably flexible, as in the Tapir, but there was evidently no true proboscis. All the known remains of the Brontotherida are from east of the Rocky Mountains, in the Miocene beds of Dakota, Nebraska, Wyoming, and Colorado. Yale College, New Haven, March 16, 1876. EXPLANATION OF PLATES. Plate X-Brontotherium ingens Marsh. Superior premolar and molar teeth; bottom view. One-third natural size. Plate XI-Brontotherium ingens. Cast of brain cavity. Figure 1, top view; figure 2, side view. One-half natural size. Plate XII-Brontotherium gigas Marsh. Lower jaw. Figure 1, top view; figure 2, front view; figure 3, side view. One sixth natural size. Plate XIII-Brontotherium. Figure 1, hind foot; natural size. figure 2, fore foot. One-sixth THE AMERICAN JOURNAL OF SCIENCE AND ARTS. [THIRD SERIES.] = ART. XLII-On supposed changes in the Nebula M. 17 = h. 2008 G. C. 4403. (R. A. 18h 12m 338.1; N. P. D. 106° 13' 36"; 1860-0); by EDWARD S. HOLDEN.* I. Historical Notes-Observations:-This nebula was discovered by Messier and is number 17 of his list (Connaissance des Tems 1784). It has been carefully studied since 1800, by Sir John Herschel (1833-37), Lamont (1837), Mason (1839), Lassell (1862), Huggins (1865), Trouvelot (1875), and Trouvelot and myself (1875). These observations, so far as they are published, are to be found in the following works: HERSCHEL: Observations of Nebulæ, etc., made at Slough; Phil. Trans., 1833, p. 498 and Plate XII, fig. 35. HERSCHEL: Results of Astronomical Observations at the Cape of Good Hope, p. 8 and Plate II, fig. 1. LAMONT: Ueber die Nebelflecken, 1837, fig. X. LAMONT: Annalen der K. Sternwarte bei München, band xvii, p. 332 and fig. 21, MASON: Transactions American Phil. Soc., vol. vii, 1840, p. 165, Plate VI. HUGGINS: Philosopical Transactions 1866, p. 385. The later observations are unpublished. I extract from these various authorities such portions as will be of use for subsequent reference. From Herschel's paper (Phil. Trans., 1833):— "The figure of this nebula is nearly that of a Greek capital omega,, somewhat distorted, and very unequally bright. Messier perceived only the bright [eastern] branch of the nebula now in question, without any of the attached convolutions which were first noticed by my father. The chief peculiarities which I *This article has in part appeared in the Popular Science Monthly; and this Journal is indebted to Messrs. Appleton & Co. for all but one of its excellent illustrations. AM. JOUR. SCI.-THIRD SERIES, VOL. XI, No. 65.-MAY, 1876. have observed it it are-1. The resolvable knot in the [eastern] portion of the bright branch, which is in a considerable degree, insulated from the surrounding nebula; strongly suggesting the idea of an absorption of the nebulous matter; and, 2. The much feebler and smaller knot at the [northwestern] end of the same branch, where the nebula makes a sudden bend at an acute angle. With a view to a more exact representation of this curious nebula, I have at different times, taken micrometrical measures of the relative places of the stars in and near it, by which, when laid down as in a chart, its limits may be traced and identified, as I hope soon to have better opportunity to do than its low situation in this latitude will permit." From Ast. Obs. at the Cape of Good Hope:-After explaining that his first figure is far from accurate Herschel says: "In particular the large horseshoe shaped arc... is there represented as too much elongated in a vertical direction and as bearing altogether too large a proportion to [the eastern] streak and to the total magnitude of the object. The nebulous diffusion, too, at the [western] end of that arc, forming the [western] angle and base-line of the capital Greek omega (2), to which the general figure of the nebula has been likened, is now so little conspicuous as to induce a suspicion that some real change may have taken place in the relative brightness of this portion compared with the rest of the nebula; seeing that a figure of it made on June 25, 1837, expresses no such diffusion, but represents the arc as breaking off before it even attains fully to the group of small stars at *For the use of the cuts which are given with this article, I am indebted to the courtesy of Dr. Youmans, Editor of the Popular Science Monthly. |