424 CRANIA FROM THE MOUNDS OF FLORIDA. 



squamosa which lies back of the auditory meatus. The temporal bone back of the 

 post-squamosa is here denominated the ecto-petrosal portion. 1 



The mastoid region as usually outlined thus disappears and in its place two 

 subregions are named for the temporal bone back of the auditory meatus, namely, 

 the post-squamosal and the ecto-petrosal portions. The remains of the suture 

 between the two is often denned. — In the ecto-petrosal portion near the line of 

 union with the parietal, the temporal bone is relatively thin and resembles that else- 

 where seen in the cranial vault, The outer surface is distinguished by grooves for 

 veins, the intervals between them being often spiculate. These vein-tracks are 

 deep, closely aggregated and since they present an appearance as though the 

 surface was worm-eaten, I have used the word serpiginous in describing this portion 

 of the skull. The entire region lies well on the norma lateralis in the clolicocephalic, 

 but is carried round to the norma occipitalis in the braclrycephalic skulls. The 

 suture between the post-squamosal and the ecto-petrosal portions reaches the upper 

 border of the bone. 



In a general way it may be said that the line of junction of the temporal 

 elements with the posterior-inferior angle of the parietal bone is made up as follows : 

 the anterior one-fourth is post-squamosal and the posterior three-fourths are ecto- 

 petrosal. The divisions of the pars squamosa, as a rule, unite abruptly- but they 

 may pass into one another without " break " when the squamosa is said to be inclined. 



Since the line of junction of the post-squamosal portion with the parietal bone 

 is also the crest of the endo-petrosal portion as it abuts against the base of the cranial 

 vault (a correlation which can be easily determined by the finger passed within the 

 foramen magnum), the precise relations of the post-squamosal with the ecto-petrosal 

 can be determined in the skull at airy age. It is occasionally indicated by a bold 

 process of the parietal which in this essay is called the mortise. I have ascertained 

 that in a fragment of any skull in which the zygoma, the post-squamosal and the 

 ecto-petrosal are destroyed, the horizontal plane of the skull can be established by 

 taking the point above named as one factor and the line of the impression of the 

 external pterygoid muscle on the angle of union between the ascending and hori- 

 zontal limb of the alisphenoid (infra-temporal crest), as the other. 2 



The variations in the squamosa, especially those seen in the transition from 

 childhood to maturity, are sometimes marked. I have, therefore, measured the 

 height, taking the distance from the post-zygomatic ridge at the mid-point over the 

 external auditory meatus to the highest part of the parieto-squamosal suture. 



1 Huxley proposed a scheme of periotic bones for vertebrates in which he identified a pre-otic, an 

 epi-otic and an opisthotic element, These identifications have not been sustained (see H. C. Chapman, 

 Proc. Acad. Nat. Sci., Phila., 1894). The word periotic is definite enough and is synonymous with pars 

 petrosa, since it is found-that this element in the immature bone reaches the periphery in the lower part 

 of the squamoso-occipital interval. But in human anatomy the bony cochlea and semi-circular canals 

 become invested with a specially compact bone of pyramidal form whose base is adjusted to the side of 

 the skull in an abrupt and definite manner. The peripheral extension is here called the ecto-petrosal, 

 since a name is needed in an attempt to displace, at least in morphological studies, the incongruous 

 "mastoid." 



2 Report of the Association of American Anatomists, 1893. 



