358 PROFESSOR OWEN ON THE GENUS DINORNIS. 



postfrontals, from which the supraorbital ridges converge to the antorbital processes. 

 The whole upper surface of the cranium (fig. 2) presents a shght and little-varied con- 

 vexity, and is bounded by a hexagonal periphery ; the two middle angles formed by the 

 postfrontals (12) and the two posterior angles formed by the paroccipitals (4) being most 

 produced, especially the latter, and each of the three sides bounded by them being 

 largely excavated ; the lateral ones by the temporal fossse (s), from which the small 

 mastoids project to join the postfrontals ; and the posterior one by the festooned 

 exoccipital arch (3, 3), below which the condyle (i) projects ; the anterior border is also 

 excavated or encroached upon by the naso-premaxillary base of the bill (is, 22') : the 

 two antero-lateral or orbital borders (a to 12) are nearly straight. 



No known bird presents such characters of the upper surface of the cranium : 

 those of the lower surface (fig. 3), afforded by the occipito-sphenoidal wedge (5, 5') , by the 

 abutment against its recurved borders of the thick paroccipital ridge (4'), and by the 

 articulation or anchylosis of the stylohyal (ss) with the mesial extremity of this ridge, 

 form still more striking peculiarities of the Dinornis, or at least of the species under 

 consideration. It is rare to see in a bird's cranium the roof of the orbit convex at its 

 mesial half, pressed down, as it were, by the cerebral lobes above : this is the case with 

 the Dinornis (fig. 3, 10,11), where the convexities are divided from the presphenoid by a 

 wide and moderately deep channel. The rough surface for the origin of the ' pro- 

 tractor tympanici ' muscle (orbito-quadratus, V. d'A.) is remarkably well defined along 

 the back-part of the orbit, extending from the alisphenoid to the under surface of the 

 postfrontal ; the fore-part of this long tract is indented by the fascicuh of the muscle, 

 which was probably implanted into the large and deep depression on the inside of the 

 orbitar process of the tympanic. The upper surface of the basioccipital presents two 

 lateral depressions divided from each other by a median longitudinal ridge, and bounded 

 laterally by precondyloid foramina. 



The inner surface of the petrosal forms a smooth convex border around a deep fossa 

 (16, fig. 7) ; below which is a slight depression with the minute foramina for the passage 

 of the acoustic nerve {ac) to the labyrinth. The bottom of the petrosal pit, which is 

 half an inch deep, and two lines wide at its mouth, appears to be naturally perforated 

 by one or two minute foramina communicating with the pneumatic diploe. It gives the 

 shape and degree of development of the lateral lobes of the cerebellum of Dinornis. The 

 upper half of the petrosal border is bounded by a channel, narrow and deep at its middle 

 part, terminating behind close to the foramen magnum and expanding in front into a 

 wider depression for the optic lobes (/), in which both the foramen ovale {tr) and foramen 

 rotundum are perforated : this depression is bounded above by the sharp tentorial ridge 

 (t). The supraoccipital is deeply impressed by the cerebellum, and this fossa is defined 

 above by a broader and blunted continuation of the lateral tentorial ridges : there is no 

 osseous falx ; only a slight median obtuse ridge where the frontal suture existed. The 

 ' canalis caroticus ' (c, fig. 4), commencing from the same external depression as the pre- 



