FOSSIL AND RECENT 



133 



premaxilla head to the dorsal margin of the dermethmoid ridge. This ligament, the 

 tight fit of the articulatory facet and the presence of tough connective tissue combine 

 to make the premaxilla practically immovable. The lateral surface of the premaxilla 

 is perforated by three or four pores which lead to a sensory canal running through 

 the bone. Posteriorly the alveolar process of the premaxilla is tapered and received 

 in a small notch in the maxilla. 



The maxilla is narrow and stout anteriorly where it curves inwards to articulate 

 with the ethmoid via a biconcave cartilaginous pad. Posteriorly the maxilla is 

 thin and ovoid in lateral view, save for a small excavation into which a single oval 

 supramaxilla fits. 



The majority of the upper jaw teeth are found on the premaxilla. The oval 

 margin of the premaxilla is clothed with many small needle-like teeth which point 

 towards the buccal cavity. The maxilla has a feeble dentition, there being only five 

 or six pointed teeth set in a single row. 



Mandible. The mandible is short and deep with a prominent coronoid process 

 situated anteriorly. Ventrally the margins of the dentary and articular are in- 

 flected and form a broad shelf. From the lateral face of this shelf a thin flange of 

 bone projects and this forms a partial protection for the mandibular sensory canal. 



The dentary is narrow anteriorly and is markedly turned inwards at the symphysis. 

 In shape, size and disposition the numerous dentary teeth resemble those on the 

 premaxilla. 



The articular is slightly larger than the dentary. Posteriorly it forms the outer 

 aspect of the articular facet. The endochondral articular (endosteal articular of 

 Ridewood 1904) is distinguishable by the spongy nature of the bone but it appears 



dsp 



hm 



m ros 



sop 



pmx 



10mm 



den 



art lo 3 



pop 



Fig. 66. Pterothrissus gissu Hilgendorf. Cranium in left lateral view. 



