The zoology of the voyage of H.M.S. Beagle [vol. 1 of 5] : $b Fossil mammaliaOwen, Richard
Science
The zoology of the voyage of H.M.S. Beagle [vol. 1 of 5] : $b Fossil mammalia
Owen, Richard
Beagle Expedition (1831-1836); Mammals, Fossil; Paleontology -- South America; Zoology
The remains of the anterior extremity of our Macrauchenia include
fragments of a left scapula; the proximal extremities of the anchylosed
bones of the right antibrachium; the metacarpal and most of the
phalangeal bones of the right fore-foot. The first-mentioned fragments,
include the head and neck of the scapula, a small part of its body with
the beginning of the spine, the coracoid process, and the nearly entire
glenoid cavity. This articular surface (fig. 2, Pl. IX.) resembles in
its general form, and degree of concavity, that of the Camel and
Rhinoceros, and is deeper than in the Hippopotamus. The coracoid process
is represented by a slightly produced rough, thick, and obtuse
tuberosity, situated closer to the glenoid cavity than in the _Camelidæ_
or _Rhinoceros_, and having almost the same relative position and size,
as in the _Palæotherium crassum_. The superior border or costa of the
scapula presents much variety in the Ungulate quadrupeds with which we
have to compare the Macrauchenia. In the Ruminants its contour forms
behind the coracoid a concave sweep, which advances close to the spine
of the scapula. In the Camel and Horse the marginal concavity is
shallower, and the distance of the superior costa from the spine of the
scapula is greater; the extent of the supra-spinal fossa increases in
the true Pachyderms, and the Macrauchene agrees with them in this
structure. In the Tapir, however, the contour of the superior costa is
broken by a deep round notch immediately behind the coracoid: in the
Hippopotamus this process arches in a slight degree backward over a
corresponding but wider and shallower notch. In the _Palæotherium
crassum_ the concavity of the superior costa, behind the coracoid, is as
slight as in the Rhinoceros; but in the Macrauchenia the superior costa
of the scapula begins to rise or stretch away from the parallel of the
spine, immediately behind the coracoid process. The modifications of the
spine of the scapula which characterize respectively the Ruminants and
Pachyderms have been clearly and concisely set forth by Cuvier, who at
the same time points out the exceptional condition which the _Camelidæ_
present in the production of the acromial angle. It was with peculiar
interest and care, therefore, that I reunited all the fragments of the
scapula of the Macrauchene, in the hope of gaining from this part of the
skeleton as decisive evidence of an affinity to the Camel as the
cervical vertebræ had afforded. It unfortunately happens, however, that
the part of the scapula most important in this comparison is broken off;
yet from this very circumstance, combined with a slight inclination
forwards of the anterior margin of the spine immediately beneath the
fractured acromion, and from the thickness of the fractured surface, we
may infer that the acromial angle of the spine was more produced than in
the ordinary Ruminants, although evidently in a less degree than in the
Camel tribe.
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