On the archetype and homologies of the vertebrate skeleton / by Richard Owen.

  • Richard Owen
Date:
1848
Catalogue details

Licence: Public Domain Mark

Credit: On the archetype and homologies of the vertebrate skeleton / by Richard Owen. Source: Wellcome Collection.

Provider: This material has been provided by King’s College London. The original may be consulted at King’s College London.

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    ,d pleurapophyses are occasionally ossified from two centres in the great -tortoises of India and the tlalapagos isles. The free extremities of the t cervical pleurapophyses of crocodiles and plesiosaurs are expanded and it luced forwards and backwards, like axe-blades, whence the name of '! chet-bones,’ applied to them prior to the recognition of their true homo- i- he pleurapophyses are appended sometimes simj)ly to the ends of par- « ohyses; sometimes to the ends of diapophj-ses; sometimes by a head and i- rcle to both kinds of transverse processes; sometimes directly to the Ji of the centrum; and sometimes they are shifted backwards over the in- ertebral space, and are articulated equally to two centrums (human lax), and sometimes to two centrums, to a neurapophysis and to a long U ^ophysis, as in the sacrum of the ostrich (fig, 27, pi)- In the atlas of if ^ fishes the pleurapophysis is detached from its centrum, and is suspended, i its hsemapophysis, from the antecedent haemal arch (scapiilo-coracoid). oonie sturgeons the abdominal pleurapophyses are composed of two or I e cartilaginous pieces. I have observed some of the expanded pleurapo- : kses in the great Tesludo elephantopus ossified from two centres, and the ; Iting divisions continuing distinct but united by suture. The pelvic r. rrapophysis is in two pieces, as a general rule (fig. 28, pV attached to i- ; and the lower piece is the seat of that most common and simple kind .1, lodification, viz. increase of size with change of form from the cylindrical ; - flat bone (as indicated by the dotted line in fig. 27), whereby it comes a connection with the pleurapophyses of other vertebrte besides the proxi- c piece of its own; such pleurapophyses having their development stunted -s not to exceed in size the proximal portion of the pelvic pleurapophysis, :• >cse expanded distal portion (es) receives the special name of ‘ ilium.’ This i;: 2 retains its rib-like shape however in the chelonians, as in the batrachians: lost species it unites below with two haeinapopbyses, called, on account ;; .heir modifications of form and proportions, ‘ischium ’ and ‘pubis.’ The j .nrapophyses defend the haemal or visceral cavity ; they are the fulcra of ..moving powers which expand and contract such cavity in respiration, [ .'.n its walls admit of those movements ; they frequently support ‘ diverging I ;3ndages,’ and give origin to muscles moving such appendages, or acting .; n the vertebral column. In some exceptional cases the pleurapophyses I ame, themselves, locomotive organs, as in serpents and the Draco volans. .'he hremapophyses, as osseous elements of a vertebra, are less constant than pleurapophyses; although they sometimes exist in segments, e. g. the : -bar vertebrae of certain saurians, and in the case of the ischium, or second ■ ic baemapophysis, in which the corresponding pleurapophyses are absent, V short, or anchylosed to the transverse processes. The only true bony napophyses in the trunk of fishes appear to be those of the atlas, forming ] lower piece of the epicoracoid ; and of the last(?) abdominal vertebra, i ning the ischial or pubic inverted arch supporting the appendages called i ntral fins.’ It is at least to the last abdominal vertebra solely that the lologous arch and appendages are connected, by the medium of the irapophyses (iliac bones) in the batrachians, and it needs but the removal ' he pleurapophysis, or of its second complementary portion {pV in fig. , to reduce that vertebral segment to the condition which it presents in an orninal fish. 'I'be so liberated inferior (haemapophysial) portion of the /ic (last abdominal costal) arch is subject, in fishes, to changes of position more extensive than liave been observed in the neurapophyses or pleur- physe.s of the trunk-vertebrae, without however preventing the recognition he segment to which such shifted limmapophyses acrtually and essentially It 2