(1) The frequency of occurrence on the left and right sides only, and on both sides of the skull, and the size, of the varietal, Mastoid, Condyloid Emissary Foramina and the Foramen of Vesalius are summarised individually on pages 22, 31, 44 and 48.
(2) The Condyloid Foramen is the most constantly present of all the emissary foramina, (present on one or both sides in 77 %. cases), and the largest in size, (bore 1.5 mm. or over in 70%). The Mastoid Foramen comes next in frequency(68%), and in size (1 mm. or over in 66%), followed by the Parietal .Foramen (present in 60%; bore .5 mm. or in 50% under). The Foramen of Vesalius is the least commonly present (36.5%), and is the smallest in size (bore .5 mm. or under in 65%).
(3) There is no difference in the age incidence of the emissary foramina.
(4) There is no difference in the sex incidence.
(5) Racial Differences. There is a marked contrast between Australians and other races, especially the White races, in the dis- tribution and size of the emissary foramina. Whereas in White races, the parietal foramina are more frequently absent than in other races, these for- amina are quite common in Australians, and are larger in size, especially as compared with White races. iledian parietal foramina are relatively more com- mon in Australian and Ne;; Zealand skulls, especially when compared with White races. The mastoid foramen is less commonly present in Australians, and when present is decidedly smaller than in White races. The condyloid foramen is less frequently found in Australians, and is also smalrer than in other races. In 3.510 skulls, there were no emissary foramina present at all. This figure was higher in African races (6.2), and still more in Australians (7.7°A).
(6) These differences in the distribution and size of the emissarty foramina in Australians correspond to the arrangement found in the Simiidae, and are prob- ably to be considered "Simian characters".
(7) The Foramen Caecum was definitely patent only S times in 212 skulls, the interior of which could be examined, that is in 1.t , If in addition, doubtful cases are included, this figure is brought up to 5%. Even so, the condition is much less common than the text books would have one believe.
(8) An Occipital Emissary Foramen in the region of the external occipital protuberance was present on 2'+ occasions, in 1.7 %0 skulls. Cases are quoted where it has been of considerable size.
(9) A rostglenoid or. Squamosal Foramen was found in 8 skulls (u.52). This foramen is normally constantly present in certain animals, but is rarely found in the Simiidae.
(10) Differences in the arrangement of the emissary foramina. in Ean and Animals were noticed, and a com- parison is made on pages 156 and 1Y1. The Simians appear to occupy an intermediate position between the other Anthropoids and Man, being similar to Man in that the rarietal Foramen is not uncommonly present, although always single, while the r ostglenoid Foramen is practically always absent. They tend to resemble Australian sk a.11s in the particulars already noted as "Simian Characters ". These differences may be associated with the 'difference in size of brain and cranial capacity in Nan and Animals. The emissary foramina are on the whole less common in Animals than in Man, and in certain classes of animal they are altogether absent.
(11) Abnormally large parietal foramina may be met with. They are probably due to a defect in the ossification of the parietal bones and are apparently not associated with an enlarged parietal emissary vein. Their existence must be remembered clinically and differentiated from other deficiencies in the skull-cap. There is a large literature on the subject.
(12) Abnormally Large Mastoid Foramina may be met with, and appear to be associated with an enlarged mastoid emissary vein, which may take the place of the Transverse Sinus. One case of Abnormally Large Mastoi Foramen has been recorded with seven other instances from the literature.
(13) There is an important relationship between the emissary foramina and the diploic veins of the skull. There is evidence that they communicate to a greater or less extent in probably the majority of cases. When the emissary foramen is absent, its place is frequently taken by a diploic opening. In the mastoid region, the posterior temporal diploic vein may have a common orifice with the mastoid emissary vein on the external or internal aspect of the bone. By means of their communications, diploic veins may indirectly become emissary veins.
This relationship is probably of importance in the spread of infection from the exterior of the skull.
(14) Little has actually been recorded of the spread of infection by the parietal, Mastoid and Condyloid foramina, but theoretically on anatomical grounds, they would appear to be important paths of infection to the cranium and its contents. This question deserves further consideration from the clinical standpoint.
(15) Radiologically the Diploic Veins appear to be ore important than the emissary foramina, as in the Diagnosis of certain types of Brain Tumour. The normal appearances of these veins must also be remembered before making a Diagnosis of fracture of the cranial vault.
(16) Normally only the Condyloid Emissary Veins are likely to give rise to serious haemorrhage during operations. The Mastoid Veins may, however, do so if enlarged, and in rare cases, the haemorrhage may be as serious as that resulting from wounding the Transverse Sinus itself.
