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No. 11.—SQUAMOSAL BONE IN TETRAPODOUS 
VERTEBRATA. 1 
m&rary 
BY F. W. THYNG. 
botanical 
Introduction. GAnDSL. 
One of the most vexed questions of comparative osteology is that 
of the homologies of the squamosal bone throughout the vertebrates. 
Slight study of the literature shows that the name squamosal has been 
applied to several bones while the bone which, as I hope to show, is 
the homologue of the human squamosal, has had a number of names. 
The term squamosal, including its various forms, was first applied 
to an element in the human skull which later fuses with others to form 
the temporal bone. Hence in applying the term to the lower groups 
the laws of nomenclature demand that it be given to that element 
alone which is the homologue of the squamosal in man. It is also 
evident that all possible criteria should be utilized in settling these 
homologies, not alone those of adult relationships and articulations 
but those of development as well. 
The relations of the squamosal in the adult Mammalia differ 
slightly in the several orders, but nowhere is there the slightest doubt 
as to its homologies with the element in man. In general it may be 
defined as follows. It is a bony lamina usually sharing in the forma¬ 
tion of the lateral wall of the brain case, but occasionally excluded 
therefrom when the periotic extends to the temporal. It articulates 
anteriorly with the alisphenoid, and sometimes with the frontal; dor- 
sally with the parietal; posteriorly with the exoccipital and the mastoid 
portion of the petrosal; and ventrally with the tympanic and the 
petrosal. From its lower anterior angle it gives rise to a zygomatic 
process which articulates with the jugal (when present) and which 
bears on its ventral surface the glenoid fossa, bounded posteriorly 
in many forms by a well marked postglenoid process. This zygomatic 
process forms the external posterior border of the temporal vacuity. 
In man the squamosal is indistinguishably fused to the petrosal and 
QZ 
CL 
Contributions from the Biological laboratories of Tufts college. No. XLIV. 
