CLASSIFICATION, AND PHTLOGENT OF THE DINORNITHID^. 389 



V. The ethmoidal region. (Plate LVI. figs. 3 & 4 ; Plate LVII. figs. 7 & 8 ; Plate 

 LVIII. figs. 11-13; Plate LIX. figs. 16-18.) 



The mesethmoid (figs. 16 & 18, mesetli.) is a vertical plate of bone ankylosed in 

 the adult by its whole ventral border to the rostrum, continuous behind with the 

 presphenoid, and having its dorsal border sloping from behind forwards immediately 

 beneath the nasal process of the premaxilla. It is perforated posteriorly by an 

 irregular fenestra of very variable size (fig. 16), which, in the dried skull, places the 

 two olfactory chambers in communication with one another. 



The olfactory chambers thus connected form a spacious cavity lying beneath and in 

 front of the anterior portion of the cranial roof and extending nearly as far back as the 

 optic foramen. Postero-dorsally they are perforated, on each side of the middle line, 

 by one or sometimes two rather irregular apertures which serve for the passage of the 

 olfactory nerves. Their roof and side-walls are formed by the lateral or ectoethmolds, 

 which are divisible into three principal parts. The first, or superior aliethmoid 

 (figs. 17 & 18, sup.al.eth.) extends almost horizontally outwards on each side from 

 about the posterior half of the dorsal border of the mesethmoid, underlying the 

 nasals and the anterior part of the frontals (fig. 16) and forming the roof of the 

 olfactory chambers. Tiie second portion, or inferior aliethmoid (fig. 18, inf.al.eth.), 

 is a concavo-convex plate forming the side-wall of the posterior part of the chamber, 

 continuous behind with the pre- and orbitosphenoids, and in the young skull articu- 

 lating by suture with the orbital plate of the frontal. 



These two are the only parts of the ectoethmoid retained in the majority of Moa 

 skulls, but in good specimens there is to be seen more or less of the third portion of 

 the ectoethmoid known as the antorlital plate (prefrontal, Huxley), and corresponding 

 with the dilated part of what I have called the fifth portion of the ectoethmoid in 

 Apteryx (24). This consists of an upright plate of thin bone (figs. 3 & 7, a.orb.) 

 placed somewhat obliquely in the front part of the orbit ; its mesial border is 

 continuous with the inferior aliethmoid, and its lateral border is ankylosed to the 

 lacrymal. It is continued forwards (in Emeus, species a) beyond its ankylosis with 

 the lacrymal by a thin scroll-like bone, the alinasal (figs. 3, 4, 7, & 8, al.n.), which 

 nearly meets above with the superior aliethmoid and below with the triangular process 

 described on page 390. The ossified posterior turbinal (figs. 6 & 8, turh.) is an 

 ingrowth from the posterior end of the antorbital. 



The lacrymal (figs. 7 & 8, lac.) is completely ankylosed with the lateral border of 

 the antorbital, is deeply notched, or in Anomalopteryx didiformis perforated, for the 

 lacrymal duct, and presents below an oblique facet for articulation with the maxilla. 

 The maxillary process of the nasal, or maxillo-nasal oi Emeus, lies immediately in front 

 of and parallel with the lacrymal, converting the notch into a foramen {lac. for.). 



In Dinornis the antorbital is a much stouter bone than in the other genera, and is, 

 therefore, more frequently found intact. It is much narrower than in the remaining 

 forms, owing to the great size of the supraorbital fenestra (see p. 390), and is sloped 



VOL. XIII. — PART XI. No. 3. — October, 1895. 3 k 



