SKELETON OE PHOROEHACOS LNELATUS. 



63 



inner capitulum (I.H.) is borne on a thin, backwardly-directed buttress of bone; it has 

 two facets, one nearly flat, looking upward and inward, the other convex and directed 

 downward. The neck of the bone is deeply excavated by pneumatic fossae, both on its 

 anterior and posterior face, and also on the inner side at the base of the orbital process 

 (O.P.). This latter is large ; its upper and lower borders are nearly parallel, and it 

 terminates in a roughened surface; its length is about 17 mm. 



Fig. 2. 



O.H 



O.P 



I.H. 



Left quadrate of Phororhacos inflatus Ameghino. 



1. Erom outer side. 



2. Articular surface for mandible. 



3. Erom front. 



inner head ; I., inner articular surface for mandible ; J.C., cup for end of jugal arch ; 0., outer articular 

 surface for mandible ; O.H., outer head ; O.P., orbital process ; P.T., tuberosity for articulation 

 with the pterygoid. 



The lower end is massive and bears two articular surfaces (I. and O.) for the mandible, 

 which are separated by a shallow groove running outward and forward from the postero- 

 internal border. The form of the facets will be best understood from the figure (fig. 2, 

 above). On the inner border of the bone, just beneath the base of the orbital process, 

 there is an elongated tubercle (P.T.) for union with the hinder end of the pterygoid ; 

 and on the outer side, immediately above the surface for the mandible, is the deep 

 circular cup (J.C.) with clearly defined border, which receives the posterior end of the 

 quadrato-jugal. 



The mandible (Plate XIV.) is specially remarkable for its very massive structure. 

 The relatively narrow symphysis is about 9 cm. long; its ventral border is convex, its 

 dorsal nearly straight, and but slightly upturned at the top. The upper surface 



vol. xv. — part in. No. 2. — October, 1899. l 



