On the Archetype and Homologies of the Vertebrate Skeleton

author, 1848 - 203 Seiten
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Seite 58 - autogenous" elements. The italics denote the parts, more properly called processes, which shoot out as continuations from some of the preceding elemente, and are termed 'exogenous': eg the diapophyses or upper ' transverse processes,' and the zygapophyses, or the ' oblique ' or ' articular processes ' of human anatomy. The autogenous processes generally circumscribe holes about the centrum, which, in the chain of vertebrae, form canals. The...
Seite 58 - He becomes the true discoverer who establishes the truth : and the sign of the proof is the general acceptance. Whoever, therefore, resumes the investigation of a neglected or repudiated doctrine, elicits its true demonstration, and discovers and explains the nature of the errors which have led to its tacit or declared rejection, may calmly and confidently await the acknowledgments of his rights in its discovery.
Seite 10 - Draco volans ' offers a good illustration of both relations. Its fore-limbs being composed of essentially the same parts as the wings of a bird are homologous with them ; but the parachute being composed of different parts, yet performing the same function as the wings of a bird, is analogous to them. Homologous parts are always, indeed, analogous parts in one sense, inasmuch as, being repetitions of the same parts of the body, they bear in that respect the same relation to different animals. But...
Seite 9 - There exists doubtless a close general resemblance in the mode of development of homologous parts ; but this is subject to modification, like the forms, proportions, functions and very substance of such parts, without their essential homological relationships being thereby obliterated. These relationships are mainly, if not wholly, determined by the relative position and connection of the parts, and may exist independently of form, proportion, substance, function and similarity of development.
Seite 8 - The term is used by logicians as synonymous with ' homonyms,' and by geometricians as signifying ' the sides of similar figures which are opposite to equal and corresponding angles,' or to parte having the same proportions t : it appears to have been first applied in anatomy by the philosophical cultivators of that science in Germany. Geoffroy St. Hilaire says, " Les organes des sens sont homologues, comme s'exprimerait la philosophie Allemande ; c'est-à-dire qu'ils sont analogues dans leur mode...
Seite 70 - Amongst air-breathing vertebrates the pleurapophyses of the trunk segments are present only in those species in which the septum of the heart's ventricle is complete and imperforate, and here they are exogenous and confined to the cervical and anterior thoracic vertebrae.
Seite 113 - It has been abundantly proved, I trust, that the idea of a natural segment (vertebra) of the endoskeleton, does not necessarily involve the presence of a particular number of pieces, or even a determinate and unchangeable arrangement of them. The great object of my present labour has been to deduce, by careful and sufficient observation of Nature, the relative value and constancy of the different vertebral elements, and to trace the kind and extent of their variations within the limits of a plain...
Seite 71 - ... is counted as a single component bone of the skeleton, is sufficiently obvious. The os innominatum is represented throughout life in most reptiles by three distinct bones, answering to the iliac, ischial, and pubic portions in anthropotomy. The sternum in most quadrupeds consists of one more bone than the number of pairs of ribs which join it ; thus it includes as many as thirteen distinct bones in the Bradypus didactylm. The arbitrary character of the definition of a bone, as ' any single piece...
Seite 10 - ANALOGUE." — A part or organ in one animal which has the same function as another part or organ in a different animal. " HOMOLOGUE." — The same organ in different animals under every variety of form and function f.
Seite 58 - ... this knowledge is the determination of the vertebral segments, or natural groups of bones, of which the myelencephalous skeleton consists. I define a vertebra, as one of those segments of the endo-skeleton which constitute the axis of the body, and the protecting canals of the nervous and vascular trunks : such a segment may also support diverging appendages.

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