172 Scientific Proceedings, Royal Dublin Society. 



on the outside of the skull, being concealed by the opisthotics and 

 parasphenoid. 



The mesethmoid^ consists of a pyramid-shaped portion and a 

 process, which stretches backwards from this to articulate with the 

 frontal. The base of the pyramid rests on cartilage, which sepa- 

 rates it from the Yomer and prefrontals. The hone, however, 

 touches the vomer in front, and two processes behind bridge over 

 the cartilage and join the prefrontals. From the apex of the 

 pyramid strong ligaments pass downwards and outwards to the 

 maxillas, and the maxilla articulates with a cavity formed by the 

 mesethmoid and vomer and the cartilage between them. 



The vomer, viewed from below, is shaped something like an 

 arrow-head, the barbs pointing backwards. In front there are a 

 few teeth attached to this (the under) surface. Above it articu- 

 lates with the mesethmoid, prefrontal, and parasphenoid, and, 

 curving round the anterior end of the latter bone, articulates with 

 it also below. At the side, close behind the barbs of the arrow, is 

 a depression for the attachment of a very strong ligament, which 

 connects it to the palate bone. 



The parasphenoid is a long, strong bone, stretching along 

 nearly the entire length of the base of the skull. In the middle 

 it is somewhat constricted, and of a prismatic form. 'In front of 

 this its upper margin splits, to enclose the median cartilage, and 

 the anterior fourth of the bone articulates with the vomer below 

 and prefrontal above. Behind the constricted portion a pair of 

 processes run upwards and outwards, and, articulating with the 

 prootics, bound the pit for the orbital muscles. Behind it articu- 

 lates with the opisthotics and basioccipital. 



The prefrontal i.s of a very irregular form. Behind it expands 

 into a broad, curved plate, which articulates with the frontal. On 

 the outer edge of this there is a projecting ridge, the truncated 

 end of which articulates with the lacrymal, and below this a liga- 

 ment connecting it to the entopterygoid is attached. In front of 

 this the bone narrows, and, where it joins the vomer, articulates 

 with the angle of the palate bone. Below a process stretches 

 backwards, articidating with the parasphenoid, and sheathing the 

 side of the median cartilage; and where this process joins the body 



Often called simply " ethmoid." 



