PROFESSOR OWEN ON THE GENUS DINORNIS. 309 



curved border, which does not rise above the level of the calvarium to form a crest, but 

 defines by a festooned line the occipital from the coronal surface. A broad and deep 

 depression separates the condyle on each side from the par-occipital processes (4, 4) which 

 form the posterior boundary of the tympanic cavity (fig. 4, 2s). The broad basi-sphenoid 

 descends vertically for a third of an inch below, and at right angles with, the basi- 

 occipital, separated from the condyle by two small but deep depressions ; this develop- 

 ment of the base of the skull is peculiar to the Dinornis among Birds, and resembles 

 that in the Crocodile. 



All the sutures of the cranium are obliterated, but the foramen for the third division 

 of the fifth nerve shows that the ali-sphenoid (figg. 2 & 4, 6) ascended, as in other birds, 

 to meet the parietal {ih. 7), in order to form the so-called temporal fossa. The upper 

 boundary of each temporal fossa is well-defined, but not elevated into a ridge : a smooth 

 and very slightly convex surface of the cranium, one inch and ten lines in breadth, 

 intervenes between them : a continuation of the same surface, a flattened tract formed 

 by the parietal and mastoid (fig. 3, s, s), four lines in breadth, separates the temporal (6) 

 from the occipital fossae {d). A cellular air-diploe, from two to six lines thick, divides 

 the outer from the inner table of the cranium. 



The mutilated base of the present specimen exposes the upper border of the pituitary 

 depression, bounded posteriorly by the groove in the basi-sphenoid (fig. 4, 5) common 

 to the converging carotid canals, and anteriorly by the groove which lodged the optic 

 chiasma, and from which the optic foramina (fig. 4, 0, 0) are continued outwards and 

 forwards to the orbits (11', 11'). The outlets of the optic foramina are separated by an 

 interspace of one inch : the Apteryx, amongst existing birds, approaches nearest to the 

 Dinornis in this peculiarity ; but the Dodo most probably still more closely resembled 

 the Dinornis in the distinctness of and distance between the external outlets of the optic 

 canals. These foramina, in the present cranium, are smaller than those in the skull of 

 the Ostrich, and indicate it to have had smaller eyes, in which respect it must have 

 resembled the Dodo. The olfactory foramina are subcircular, three lines in diameter, 

 single, on each side, as in other birds, and at the anterior end of the cranial cavity separated 

 by an interspace of two lines : the olfactory cavities (fig. 4, is) extend backwards behind 

 these foramina, upon the under surface of the cranium, to within four lines of the optic 

 groove, a feature which, with the large size of the olfactory nerves, indicates a develop- 

 ment of the organ of smell approaching that most remarkable one in the Apterj^x. Of 

 the other outlets of the cerebral nerves, those for the ninth pair (the pre-condyloid fora- 

 mina, see fig. 1) are alone remarkable for any increase beyond the ordinary size. The 

 foramen rotundum (n, n, fig. 4) is distinct from both foramen ovale and foramen opti- 

 cum. The articular depression (fig. 4, 28) for the tympanic or quadrate bone is imper- 

 forate, eight lines long, from three to four lines wide, bounded externally by a short 

 angular process of the mastoid. 



The form of the inner surface of the cranium shows that the cerebral hemispheres 



