PHENACODUS. 465 



paramastoid processes are united into a short tuberosity with narrowed 

 apex. Tlie occipital crest is curved backwards, and the surface between 

 the external end of the occipital condyle and the lateral occipital crest is 

 concave. 



The premaxillary bone exposes an external face of nearl^^ equal width, 

 from the second incisor to its superior extremity at the anterior lateral edge 

 of the nasal bone. Posterior to this point the premaxillary bone does not 

 extend. The nasal bones expand posteriorly so as to occupy the superior 

 facial surface just anterior to the line of the anterior border of the orbits. 

 How far posteriorly they extend cannot be certainly determined in the 

 fossil, but what looks like the fronto-nasal suture crosses the face just in 

 front of the anterior border of the orbits. If this be the posterior boundary 

 of the nasals they do not have such a posterior extension as in P. primcevus, 

 although they are expanded in the same manner. The fronto-parietal 

 suture apparently crosses the- superior surface just posterior to the line con- 

 necting the postorbital processes. The anterior part of the malar bone is a 

 band of equal width extending along the border of the orbit to the lachry- 

 mal bone. The latter extends a little on the superior orbital border, and 

 about equally far below and above the lachrymal tuberosity for a moderate 

 width on the facial surface. The squamoso-malar suture is straight, and 

 the two elements of the zygoma terminate each in an acute angle. 



The foramen infraorbitale opens above the middle of the fourth pre- 

 molar tooth. The lachrymal foramen is within the orbit. Postglenoid 

 foramen rather large, issuing in a groove of the postglenoid process. A 

 postparietal, and a single mastoid foramen. A rather large foramen just 

 within the position of a supraglenoid foramen, above the postglenoid pro- 

 cess, and entering the squamosal bone posteriorly and inwards. Foramen 

 magnum incomplete in the specimen. 



Mandible — The mandibular ramus is not deep. Its inferior outline is 



gently convex from below the last molar tooth to the symphysis, which 



rises very gradually to the alveolar border. The inferior edge below the 



coronoid process is concave, and the border of the angle is broadly convex, 



turning gently forwards before ascending to the condyle. The external 



angle of the latter is prominent, and sends downwards a low ridge which 

 30 c 



