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Show 40 ZOOLOGY OF TilE VOYAGE OF TilE DEAGLE. . . . . f the Macrauchenia, and the almost flattened for~ ~f their cervi~al ve~tebl ~ ~ . ticular surfaces, I infer that the long neck in tlus smgul~r antednor anl puosst e;l~~~eaibeen carried in the same stiff and upright position as m qua rupee m the Vicugna and Guanaco. . · 1 t The following individual differences are observable m t~e two ce.rvic~ ~el e-brm of the Macrauchenia;- in the posterior one the supenor ~r~h .Is Widei a~ld with thicker parietes, the body is more concave below, and the mfenor transve1se processes have a more lengthened origin. Not a fragment of dorsal vertebrm, r1' b s or sternum, 1· 8 included in the c. ol-lection of the bones of the Macrauchenia; but fortunately seven lumbar. veitebrm, forming a consecutive series of the same individual as that to wluch the cervical vertebrm belonged, were obtained, all more or less fractured, but aH sufficiently perfect to demonstrate their true nature.. These ~ertebr~, although not possessing such distinctive charac~ers as ~he cervical, contnbute. by no means an unimportant element towards the IllustratiOn of .the ost~~logy of the Macrauchenia, and support the view which I have taken of 1ts affimt1es; for, although, as will be seen from the structure of its extremities, this animal must be refened to the Order Pachydermata, yet no existing species of that order has more than six lumbar vertebrre; whilst among the Ruminants it is only in the Camel, Dromedary, Llama and Vicugna, that the lumbar vertebrm reach the n~m~er seve~,the same number which characterizes the extinct annectant species m questwn. The dimensions of the vertebrm in the Macrauchenia present the same relations to the two cervical vertebrm above described, which the lumbar vertebrm of the Vicugna bear to the third, fourth, or fifth of its cervical vertebrm. But here we begin to discover modifications of form, in which the Macrauchenia deviates from the Camelidm, and approaches the Pachyderms, as the Ho1·se and Hippopotamus; and these indications become stronger as the vertebrm approach the sacrum. In the Camel, as well as in the Horse and Hippopotamus, the bodies of the lumbar vertebrm diminish in vertical extent, or become flatter, as they approach the sacrum; but this characte~· is more strongly marked in the Macrauchenia than in either of the above species. But in the Camelidm the transverse processes of the lumbar vertebrre, are elongated, flattened, and narrow, resembling ribs, except that they are nearly straight ; and this is more particularly the case with the transverse processes of the last lumbar vertebrre, which are the narrowest of all in proportion to their length, and stand freely out without touching the sacrum. The transverse processes of the lumbar vertebrre of the Giraffe resemble those of the Camel, but are relatively smaller and shorter. In the Hippopotamus the transverse processes of the lumbar vertebrre are much broader in proportion to their length than in any of the Ruminants, and they increase in breadth to the FOSSIL MAMMALIA. 41 last lumbar vertebra, which presents in addition, the following characters; each transverse process sends off ft·om its posterior margin a thickened and transver ely elongated ~rotuberance, which supports a flattened articular surface adapted to a correspondmg surface on the anterior part of the transverse process of the first sacml vcrte~ra .= it likewise presents on its anterior edge a flattened and rough surface, wluch IS closely attached by ligamentous substance to the opposite part of the transverse process of the penultimate lumbar vertebra. A similar structure exists in th~ last two lumbar vertebrre of the Rhinoceros, Tapir, and Horse. In the latter ammal, anchylosis of these articulating surfaces of the lumbar and sacral vertebrre generally takes place with age, and, judging from the character of the same surfaces in the Hippopotamus, the motion of its lumbar vertebrre upon the ~acrum may in like manner become ultimately arrested. Now m the Macrauchenia, as in the Pachyderms above cited, the transverse processe~ of the last lumbar vertebrre are of considerable thickness and extent and are joined by enarthrosis to the transverse processes of the sacrum ; but th~ bo1~Y structure of these joints would indicate that they were not subject to be obl.Iterated by anchylosis. The articular surfaces which pl'Ojcct from the postenor part of the transverse processes of the last lumbar vertebrre present a regular and s1~ooth concavity, adapted to a corresponding convexity in the transverse processes of th~ first sacral vertebra. These articulating surfaces have evidently be:n c.ov~red With ~mooth cartilage ; they present a pretty regular transverse elh~sotd form. A VIew of the three joiuts by which, independently of the two o~IIque processes, the last lumbar vertebra of the Macraucltenia was articulated With t~1e sacrum, is given in Plate VIII. fig. 1. The transverse processes of the p~sterwr lumba1: vertebra, be ides their agreement with those of the Horse and Hippopotamus m the structure just described, also correspond with them in general form, and deviate remarkably from those of the Cwnelidce in their O'reat breadth. o It will be seen that the articulations on the body and transverse processes of the last lumbar vertebra of the Macrauchenia differ fi·om the corresponding articular surfaces of the Horse, inasmuch as the middle surface is convex, while the ~wo lateral ones are .concave, and these are moreover relatively larger than either In the Horse or Htppopotamus: by this structure the trunk was more firmly locked to that segment of the vertebral column, which receives and transmits to the. rest o! the body the motive impetus derived from the hinder extremities, ':lllch are m all quadrupeds the chief powers in progression; while at the same tune. the sl~ock must have been diminished by the great extent of interposed elastic cartilages; and a certain yielding or sliding motion would be allowed between the hun bar vertebrre and sacrum. The anterior ob1ique processes of the lumbar vertebrre of the Macrauchcnia G |