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Re: Spare ribs?
On chevrons: It looks like the tuberculum was lost and
the capitula rotated down with the parapophyses (now
the chevron facets of the caudal centra). The 2 ribs
then fused at their distal ends. That's just how it
looks to me. Probably wrong. I'd like to know what the
deal is with sternal ribs...the names of their facets
and stuff. I've heard of "xiphisternal structures"
which I interpret to be sternal ribs. Not sure.
> If you look at the skeletons (such as they are) of
> the most primitive living
> vertebrates, it seems to me that the cervical ribs,
> thoracic/abdominal ribs,
> and hemal arches form a pretty continuous series
> along the vertebral column,
> and that the details of how and where they
> articulate with the vertebrae in
> various places along the column are secondary. This
> leads me to suspect that
> they arise in the same way from the same precursor
> structures during the
> ontogenetic development of the vertebrate body.
> Unfortunately, my copy of
> Romer's Osteology of the Vertebrates is buried, so I
> cannot confirm this (if
> this topic is even discussed there); but it seems
> unparsimonious for
> vertebrates to develop ribs in one set of loci and
> hemal arches independently
> in another set of loci where the ribs are not found.
> The only other thing I
> can think dinosaurian hemal arches might be is
> modified intercentra, which
> seems possible but weird.
> Any embryologists out there who might shed some
> light on this?
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