422 CRANIA FROM THE MOUNDS OF FLORIDA. 



manner with the tegmen tympania gives the impression that the whole constitutes 

 an important osseous septum which separates the temporal and zygomatic fossse 

 from the pharynx and is morphologically of a significance similar to that by 

 which the outer wall of the orbit becomes a septum separating the orbit from 

 the temporal fossa. 1 



(b). The degree of inflation of the pars petrosa on the posterior surfaces where 

 they abut against the basilar process is always noted since it does not exist in the 

 skulls of the anthropoid apes, and is often absent in the skull of the lower types of 

 man. Whenever it occurs it may be said to be an abrupt departure from psedomor- 

 phic conditions. The inflated petrosa signifies that as the skull increases in trans- 

 verse diameter (especially at its base) the petrosa tends to separate from the 

 basi-occipital and the basi-sphenoid bones, the inflation in a degree representing the 

 compensatory effort to occupy the space which would be thereby created. Infla- 

 tions are apt to be found in skulls in which the foramina lacera media are wide. 

 It must be remembered that the petrosa are never organically associated with either 

 the occipital or sphenoid bones, and if it were not for the union with the squamosal 

 and tympanic elements, would fall away from the skull in maceration as in the 

 Cetacea and in many genera of Chiroptera. 



ic). The foramen lacerum medium in Simia is closed between the petrosa and 

 the sphenoid, at a point answering to the Eustachian groove (lateral portion), but 

 open between the petrosa and the side of the basi-sphenoid (median portion). In 

 Antkropopitheacs, Gorilla and Hylobates the foramen is closed throughout. Hence 

 the opening is clearly composed of a median and a lateral part. Its peculiarities 

 should be noted in the description of every skull. 



(d). The sphenoido-tympanic fissure and suture. The line indicated in the 

 above title is nearly straight, with a disposition to be interrupted by the spinous 

 process of the . sphenoid bone, and for the oval and spinous foramina to approach 

 or be merged in the fissure. When the process crosses the line it is described 

 as overlapping. When the spinous process is large it is apt to be associated with 

 the pterygo-spinosal union. In all examples it evinces a disposition to extend 

 outward and effect a junction with the tegmen tympani at or near the end of the 

 sphenoido-squamosal suture. 2 



1 The significance of the external pterygoid plate is that of an ossified intermuscular septum 

 between the pterygoid muscles. It answers, in a way, to the power of these muscles since they can act 

 with better advantage having origin from a bony septum than from a fibrous one. We expect also to 

 find that a large external pterygoid process harmonizes with a high, wide ascending ramus to the lower 

 jaw. In the description of the lower jaw and of the pterygoid processes these two factors should be 

 associated. In like manner the pyramidal process of the palate bone extends a variable distance along 

 the inferior border of the external pterygoid plate. The extent of this process harmonizes with the 

 width of the plate. 



2 It is of interest to ascertain the changes which these characters undergo in the anthropoid apes. 

 In Simia the spinous process is absent and the oval foramen is almost in the sphenoido-petrosal 

 fissure ; the scpjamoso-tympanic suture is without visible tegmen in the adult ; in the young, however, 

 the tegmen is seen. The inner border of the glenoid cavity is not produced below the level of the 

 sphenoid bone. No trace of an opening answering to the foramen spinosum is present, the middle 

 meningeal artery probably passing through the large oval foramen. In Anthrojjopithecus spinous the 



