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Re: Osteological Question

I have a question about the processes bordering the temporal fenestra of a synapsid. I teaching myself osteology so I hope I can explain myself adequately.

The temporal fenestra is bordered by three bones; the postorbital, the jugal and the quadratojugal. Looking at the fenestra in lateral view the jugal looks like an upside down T (triradiate) the >anterior process is the 'suborbital process', the posterior process is the 'subtemporal process' and the dorsal process is the 'postorbital ramus' (I assume 'ramus' because it helps separate the orbit >from the temporal fenestra). The postorbital looks like a T and the quadratojugal a backwards facing c. My questions are:

Do any of the following have specific names

1) What is the ventral process of the postorbital, which together with the postorbital ramus of the jugal forms the postorbital bar, called?

Standard anatomical practice these days -- sadly, contrary to what one often sees in the literature -- is to refer to various processes of skull bones with respect to the bones with which they articulate. This means that there are NO "ventral process," "dorsal process," etc. Instead, the process you mention above would be called the "jugal process" because it articulates with the jugal. This avoids (a) problems of orientation (for example, depending on the posture one reconstructs for a skull, one person's "ventral process" could be someone else's "caudal process" or "caudoventral process"), and (b) problems of homology (for example, in your question 3 below, would the homologous process of the quadratojugal be considered "subtemporal" in something that doesn't have an infratemporal fenestra?). There are some instances where a bone sends off multiple processes that articulate with the same bone; the names given to these can be emended with directional terms (e.g., "dorsal postorbital process" and "ventral postorbital process," although this does re-introduce the directional problem, but to a lesser extent).

2) What is the posterior process of the postobital, the process that sutures to the quadratojugal, called?

The quadratojugal process.

3) Do the dorsal or ventral processes of the quadratojugal have special names? I would guess that the ventral process would be called the 'subtemporal process of the quadratojugal' and together >with the subtemporal process of the jugal form the 'subtemporal bar'.

If I am correctly understanding what you are asking, they would be the postorbital and jugal processes, respectively.

Jerry D. Harris
Director of Paleontology
Dixie State College
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