390 PEOF. T. JEFFERT PAEKER ON THE CRANIAL OSTEOLOGY, 



obliquely forwards from its lower edge ; it is firmly ankylosed to the inferior aliethmoid 

 as well as to the lacrymal. Its ventral border, instead of being thin and delicate, 

 takes the form of a stout transverse ridge or bar of bone forming the posterior boundary 

 of the aperture between the olfactory chamber and the posterior nasal passage. This 

 postchoanal bar, as it may be called, is a very obvious structure when the skull is 

 viewed from below (see Owen, 19, pi. 56, or Ext. Birds of N. Z. pi. 65. fig. 1, g), 

 and constitutes a striking difference between Dinornis and the smaller genera. 



A final ectoethmoidal structure, very characteristic of the whole family, is the trian- 

 gular jiroc ess (Plate LVl. figs. 2 & 4, tri.pr.), a horizontal plate springing by a broad 

 base from the mesethmoid (fig. 18) and extending outwards at the level of the lacrymal 

 foramen. It forms the anterior boundary of the aperture between the olfactory 

 chamber and the posterior nasal passage, and its posterior border is connected by a 

 horizontal ridge with the postchoanal bar. The bar, ridge, and triangular process 

 are together called by Owen the girdle or cingulum olfactorium. 



The antorbital plate is perforated dorsally by the supraorbital fenestra. This, in 

 Dinornis torosus, is a single large aperture, more than 1 cm. in length, and continued 

 dorsad into a shallow fossa on the underside of the lacrymal (preorbital process). 

 Apparently the Hardei'ian gland fitted into both the fossa and the fenestra, the orbito- 

 nasal nerve passing through the anterior part of the latter in its passage from the orbit 

 to the olfactory cavity. Above the posterior end of the dorsal margin of the fenestra 

 is a small foramen also leading into the olfactory chamber. 



In Emeus, species « (fig. 7), the supraorbital fenestra {sup. orb. fen.) is quite small 

 and the Harderian pit (Hard.fos.) above it very deep ; posterior to these is a 

 foramen («) leading into the olfactory chamber, and beneath it a fossa (b), some- 

 times perforated. In Anomalofteryx didiformis an intermediate arrangement is 

 found ; the supraorbital fenestra is of moderate size and is connected by a wide 

 groove with a fossa in the posterodorsal region of the antorbital — this last answers 

 to fossa b in Emeus, and to the posterior moiety of the single fenestra in Binornis ; 

 above it is a small foramen answering to the similarly placed hole {a) in Pachyornis 

 and Binornis. 



In good specimens a coiled posterior turbinal (fig. 6) is seen to spring from the inner 

 surface of the posterior end of the antorbital. 



vi. The cranial cavity. (Plate LVIII. figs. 10 & 11 ; Plate LIX. figs. 15 & 16.) 

 The cavity for the brain has the usual avian form ; its length and breadth are nearly 

 equal, the greatest breadth being in the temporal region. The entire cavity may be 

 divided into the following regions : — 



a. The metencephalic fossa for the medulla oblongata. 

 j3. The cerebellar or epencephalic fossa for the cerebellum, 

 y. The mesencephalic fossae for the optic lobes. 



S. The pituitary fossa and the optic platform for the pituitary body and the 

 optic chiasma. 



