204 Proceedings of the Royal Irish Academy, 



taking the place of the spina angularis. In a Meknesian skull from 

 Chatham Island it coexisted with a fossa pterygoidea externa, protected 

 hy a strong processus pterygoidens accessorins (the same fossa I have 

 seen in the skull of a negro, and I have referred to it elsewhere) 

 (fig- 12 A). _ _ _ _ . . , 



6th. This spina sphenoidalis accessoiia may coexist with a forward 

 directed tooth on the spina angularis, and this exists in thirteen skulls. 

 In one of these, the angular tooth is pierced externally by the middle 

 meningeal artery. These two spurs often rise as sharp peaks, one in 

 front and the other behind the foramen spinosum, so as to give the 

 appearance as if the foramen bored through the spine ; this occiu's 

 in several crania, among others in one Australian, one fr-om Circassia, 

 and one found embedded in plaster, at Sinai. Sometimes the apices 

 of the two spines are joined by a bridge (that is, the band of union 

 which forms the posterior part of the connexion between the ligamen- 

 tum ptcrygo-spinosum ancl the accessoiy ligament [when these are 

 united], becomes ossified), and then there are two external outlets for 

 the foramen spinosum, an outer (larger and transmitting the artery) 

 and an inner, smaller, and usually transmitting the nervus spinosus 

 (fig. 7 a'). This may coexist with a double tooth on the eeto-pterygoid 

 process, but if so the second tooth is generally the lower, muscular, 

 one. 



7th. Cases of the formation of a complete bony bridge are not rare. 

 Professor Grruber assigns a frequency of once in tliiiieen to fourteen 

 skulls. In oiu' collection we have nine in which such a bridge occui's 

 on both sides, five in which it is present on one side. Thus our pro- 

 portion is, that a bilateral bridge exists in one in sixteen, a unilateral 

 or bilateral, once in 9.5 cases. 



Two forms of this bridge exist which should not be confounded : — 

 1 st, ossification of the true ligamentum pteiygo-spinosum. This is either 

 simple, forming a large wide arch (not a common form) (fig. 9 I p), or 

 compound, coexisting with an ossified ligamentum pterygo-spinosum 

 aecessorium. This latter form is the commonest, and, as the two liga- 

 ments are usually united for a good part of theii" extent, so the bony 

 arch is simple, wide, and shows its double natui'e by having two piers 

 at its hinder end, one continuous with the spina accessoria, one with 

 the true spina angularis (figs. 8, 11 o'). The other form is a simple 

 ossification of the ligamentum aecessorium which then forms a closely 

 adpressed arch, only bridging over the temporal and masseteric nerve, 

 (figs. 10, 13 « «). This I have seen well marked in an Esquimaux 

 skull with no spina angnilaris, and in a Cliinook skull, as well as in 

 several Irish crania. 



The ossification of the true pterygo-spinous ligament never takes 

 place autogenously. The foi'ward end ossifies by an extension into it of 

 the bony matter of the external pterygoid process, while the hinder 

 end ossifies as an offshoot fr'om the spina angiilaris ; hence where the 

 two bony growths coalesce there is, in nearly every case, a suture, 

 which I have verv seldom seen obliterated, and which is sometimes den- 



