Prof. Owen's Description of the Lepidosiren annectens. 333 



Heterohranchus, or to the ossified temporal fascia in the Ckelonire. These 

 elongated post-frontals are of a triangular form, their narrow and irregular 

 base is anterior, and is connected with the median frontal by a moveable 

 ligamentous joint : a small longitudinal vertical crest or ridge is given off 

 from the under surface. 



The analogue of the conjoined nasal and intermaxillary bones* is a strong 

 triangular plate of bone, with its rounded anterior apex forming the ante- 

 rior extremity of the skull, and supporting at its under surface the two 

 long and sharp intermaxillary teeth. It has a slight vertical movement, by 

 means of its posterior ligamentous connexions, upon the frontal and ascend- 

 ing process of the maxillary bone. The maxillary bones, palatines and ptery- 

 goids are represented by a single piece of bone on each side. The dental 

 portion of this bone presents three vertical ridges, with intervening notches, 

 radiating from the posterior part of the mesial symphysis : the ridges are in 

 the shape of compressed wedges, with the apex downwards, and are covered 

 with a continuous dense dental substance with a corresponding cutting edge: 

 an ascending triangular process of the maxillary rises above the two outer 

 dental laminae ; its apex is directed backwards, and is joined by ligament to the 

 frontal and intermaxillary bones : the external angle of the maxillary portion 

 of the bone curves backwards and ends in a free pointf. The pterygoid por- 

 tion of the bone now described is indicated by its fulfilling the usual function 

 of an abutment extended between the palatine portion of the upper jaw and 

 the articular pedicle of the lower jaw : it is expanded and compressed as it ex- 

 tends downwards and outwards to support the inner surface of the articular 

 pedicle, and terminates by a broad truncated margin;}:. 



The articular surface for the lower jaw presents a more complicated form 

 than is usually observed in either fishes or reptiles : its general contour pre- 

 sents a very regular semicircular convexity, but the surface is sculptured by 

 two parallel grooves with an intervening convex ridge, adapted to a corre- 



* Tab. XXIII. fig. 4 & 5, re n. This bone may, under another point of view, be regarded as analo- 

 gous to the rostral prolongation of the anterior part of the cranium in the Sturgeon and other Chondro- 

 pterygii ; and the true intermaxillaries may be supposed to be confluent with the maxillary, and enter 

 into the formation of the superior dentigerous arch. 



t Tab. XXIII. fig. 5, ft. X lb. fig. 4 & 5, o. 



VOL. XVIII. 2 Y 



