On Acanthopolis platypus (Seeley), a Pachypod from the Cambridge Upper Greensand / by Harry G. Seeley.

  • Harry Govier Seeley
Date:
1871
Catalogue details

Licence: Public Domain Mark

Credit: On Acanthopolis platypus (Seeley), a Pachypod from the Cambridge Upper Greensand / by Harry G. Seeley. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    pair; they do not arise quite so far forward, but extend back, widening and thickening almost to the posterior articular sur- face ; they make the widest part of the centrum. Below these ridges the sides of the centrum converge interiorly to the hypapophysial ridges; between these limits the depth of the side is inch ; above the middle of this area is a faint hori- zontal ridge which divides it into two unequal parts and gives it a convex aspect. The narrow under surface is limited by the two faint hypapophysial ridges, which slightly approxi- mate in the middle and diverge towards the two ends, termi- nating posteriorly in the oblique facet which is confluent with the posterior articulation. The posterior side is unequally six-sided, in every case a long side having a short side oppo- site to it, there being a long superior margin and a short in- ferior margin, two short sides above and two long sides be- low. Both articulations are rather conspicuously concave. In the third vertebra the centrum is equally long, but is much smaller, the posterior articulation measuring more than inch from above downward, and nearly 2 inches from side to side; while in the second vertebra the similar surface mea- sures If inch from above downward and 2f inches from side to side. In the third bone the first pair of ridges become stronger, the second become much fainter, and the obscure third ridge is now a well-marked tumid ridge : in consequence of these modifications the lateral spaces of the sides become more concave from above downward. The hypapophysial ridges have approximated much closer together, and become more elevated, especially in front, showing that the chevron bone now articulates with both the vertebrae between which it is placed ; and there is a marked increase in the concavity of this under surface from front to back. The fourth bone is badly preserved. In the fifth vertebra the length of the centrum is 2 inches; but the depth of the posterior articulation, including the chevron surface, is inch, while its width from side to side is 1-^ inch ; the lateral surfaces are markedly concave; and the whole bone looks like a substance contracted and withered. The first and second pairs of lateral ridges have disappeared; and the third ridge is now a strong elevated ridge, dividing the side into two equal parts, and at its terminations making the widest part of the articular ends. The hypapophysial ridges become parallel, rounder; and the whole under surface from back to front is deeply concave. The posterior articular surface is only slightly larger than the anterior end; and the facets for the chevron bones are nearly equal. The inter- vertebral cup is becoming less deep. In the sixth bone the centrum is If inch long. The side
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