NO. 2 A STUDY OF MENISCOTHERIUM — GAZIN 39 



prominent, elongate and broadly rounded ridge (A. on fig. 3b) on 

 both of the natural casts, corresponding in a general way to the 

 space above the broadly expanded bulge at the posterior root of the 

 pterygoid wing of the alisphenoid. It is not complete anteriorly in 

 either specimen but no doubt terminated anteromedially at the 

 sphenoidal fissure in the endocranium. The margins of this crest 

 are obscure so that details of division or possible branching are not 

 evident, and stalks for the various orifices are not preserved, but in 

 its posterior direction it turns definitely upward and outward behind 

 the pyriform lobe and adjacent to the apex of the petrosal. Because 

 of its gross size, I suspect that its total representation may be rather 

 complex, and in addition to the nerves III, IV, Vi_ 2 , and VI forward, 

 it possibly represents a cavernous sinus connecting with the ophthal- 

 mic vein forward through the sphenoidal fissure and with a petrosal 

 sinus or sinuses posteriorward behind the pyriform lobe. Posteriorly, 

 as far as can be ascertained, its position also conforms with the point 

 of entrance for the internal carotid posteromedially and with the 

 position of the foramen ovale ventrolateral^ where the third branch 

 of the trigeminal would emerge. 



On one of the casts a small portion of the surface representing the 

 medulla oblongata is preserved around the lower and left side, and 

 on the lower surface, very close to the lateral margin of the dorsoven- 

 trally compressed lateral portion, the position of the hypoglossal or 

 condylar foramen is clearly defined. A short distance anterodorsal 

 to this, at the posteroventral margin of the surface formed by the 

 petrosal is a short slightly curved ridge which denotes the cranial 

 opening of the foramen lacerum posterius. 



MANDIBLE 



The most noticeable features of the lower jaw of Meniscotherium 

 are the increase in depth of the inferior ramus posteriorward and 

 the extraordinary fanlike posterior extension of the angle (see pi. 3). 

 The two jaws are strongly united by an elongate symphysis which 

 below its posterior margin leaves a broad surface or pit for the digas- 

 tric muscle. The importance of this muscle has been attested by the 

 previously mentioned prominence of the paroccipital process. Close 

 to the symphysis on the anteroventral surface of the mandible are a 

 pair of foramina rather close to the roots of the 1st incisors. The 

 anterior of the two mental foramina is located below the first pre- 

 molar or the space between Pi and P 2 . The second mental foramen 

 is rather generally situated low beneath P 4 . The inferior dental fora- 



