202 Proceedings of the Royal Irish Academy. 



XXX. — Oif Some Foems op the Ligamen-tttm Pteeygo-spinostjm. By 

 A. Macalistee, M. B., Professor of Comparative Anatomy, Dublin 

 Uniyersity. (With Plates 19 and 20). 



[Eead April 27, 1875]. 



The bony arcli stretching from the outer pterygoid plate to the spina 

 angularis of the sphenoid bone has been described by many authors ; 

 Dieterich,^'' Grruber, Barkow as well as the manual writers have noticed 

 its existence and some of its forms. Its most common condition in 

 man as the ligamentum pterygo-spinosum has been shown by 

 Civininif and its comparative anatomy as the representative of the canal 

 or foramen present in the ecto-pterygoid plate in Bodents has been 

 abundantly referred to by these writers. 



The object of the present paper is to catalogue the very varying 

 forms of this ligament found in the skulls in the collection of the 

 Dublin University. 



The ligamentum pterygo-spinosum is an upward and forward elonga- 

 tion of the fascial fold which forms the internal lateral ligament of the 

 mandible, and usually appears as a flat band, wider at its ptery- 

 goid than at its spinous attachment, but variable in shape, lying usually 

 internal to the Arteria meningea media, external to the tensor 

 palati, which often takes an additional origin from it ; posteriorly 

 and internally it is related to the fibrous capsule of the Eustachian 

 tube, to which it is often tightly bound. 



Beside the simple ligamentum pterygo-spinosum, there exists 

 very often a second band connected with it at its pterygoid end 

 (PL 20, fig. 14 a), but inserted external to the foramen spinosum into 

 a small spur. This little process is very frequently present as a sharp 

 tooth on the outside of the oval and spiuous holes (figs. 1, 2 a), and 

 the band attached to it is much shorter, higher up, and bounds a 

 narrower archway; to this second ligament the name ligamentum 

 pterygo-spinosum accessorium is applicable, it roofs over the nervus 

 temporalis profundus and n. massetericus (fig. 14 ^' t"). This ligament 

 may be separate from the first named, or joined to it at its pterygoid 

 end, or for most of its extent, and only separated where it is pierced 

 by the middle meningeal artery and some nerve filaments. 



Of the bony arrangements coexisting with these ligaments there 

 are the following, and I have appended thereto the proportional 

 frequency of their occurrence out of 144 skulls. 



1st. The existence of the ligament with no ossified tooth on the 

 external pterygoid plate. This occurred in fifteen of the skulls on 

 both sides, and in four on one side only. In one of these the nervus 



* Dietericli, Besclireibung einiger albnormitaten dea Menschen-schadelai Basel, 

 1842, p. 9. 



t Schmidt's Jahrbiicher, l§o3. 



