338 PROFESSOR OWEN ON THE GENUS DINORNIS. 



of PI. LIII. and fig. 1 of PI. LIV. of the present Memoir with Pi. XXIII. of the Memoir 

 (Part V.) above cited. 



The mutilation of the two crania is nearly the same in kind and degree ; but with the 

 present specimen there is a tympanic bone and the mandible. 



The base of the occipital tubercle (Pis. LIII. & LIV. fig. 1, i ) is 4 lines across, 2^ lines 

 vertically ; the foramen magnum (PI. LIII. fig. 3, m) is 7 lines vertically and 6 lines across. 

 The superoccipital, or confluent upper parts of the exoccipitals, slightly overarches the 

 foramen ; the middle of the transverse occipital ridge (ib. 3) is 8 lines above the foramen, 

 and extends outward with a slight descent to the paroccipital (ib. 4), having a total 

 transverse extent of 3 inches 3 lines. The broad and low superoccipital surface, so 

 defined superiorly, is divided by a thick, low, median vertical ridge. It shows no 

 cerebellar protuberance, but four rough and shallow muscular depressions, defined by a 

 protuberant part of the middle of each half of the transverse occipital ridge. A venous 

 canal extends from each protuberance to a foramen (ib. w) near the middle of the outer 

 depression. The basioccipital (PI. LIII. fig. 3, ij) descends 5 lines below the tubercle, 

 this vertical part showing a pair of depressions (ib. & PI. LIV. fig. l,j) ; it swells out 

 below on each side into a pair of large smooth tuberosities (ib. i' ) with extremely thin 

 walls, covering the pneumatic cellular structure of the bone. 



The basisphenoid (PI. LIV. tig. 1,5) probably contributes the anterior part of these 

 tuberosities (ib. m), between which it is concave. The Eustachian canals (ib. fig. 1, e, e), 

 with sharp margins, groove the sides of the basisphenoid, converging as they extend 

 forward, and losing definition as they approach the middle of the fore part of 5. The 

 beginning of the posterior ridge forms the outer boundary of the fossa for the sym- 

 pathetic and entocarotid foramina (ib. s, c). The alisphenoid is indicated by the 

 foramen for the third and second divisions of the trigeminal nerve^ and by the fossa of 

 the optic lobe on its inner surface. The loss of the outer plate of the connate basi- and 

 pre-sphenoids exposes the pneumatic diploe and the wall (ib. d) of the ' sella ' or bony 

 cup for the hypophysial appendage of the mesencephalon, which marks the boundary 

 of the second and third cranial vertebrae. 



The mastoid (s) is large, thick, and obtuse, excavated below by a single oblong, 

 oblique articular cavity (PI. LIV. fig. 1 , u) for the undivided similarly shaped convex 

 head of the tympanic (ib. fig. 2, e) ; the articular cavity is directed from behind forward 

 and outward. There is no epiphysis upon the border of the tympanic cavity, which is 

 large, and shows several pneumatic foramina besides the stapedial fossa leading to the 

 fenestra ovalis. 



The temporal fossa (Pis. LIII. & LIV. fig. 1, 7), which excavates the contiguous parts 

 of the alisphenoid, mastoid, parietal, and postfrontal, is narrow and deep, subsiding 

 gradually upon the upper surface of the cranium (PI. LIII. fig. 1, 7), which is smooth, 

 broad, and slightly convex, for an extent of nearly 2 inches, between the fossae. The 

 whole cranium is remarkably broad and depressed (ib. fig. 3) : its greatest vertical 



