54 Zoological Society. 



occipital and basisplienoid is exaggerated, as compared with the 

 Palnpteryx, the basis cranii, which is 2| inches in length, descending 

 abruptly for the extent of 1 inch below the foramen magnum ; the 

 condyle is hemispherical as in Otis, not a quarter of a sphere as in 

 Struthio and Palaiiteryw, nor, as in Didus, a transverse reniform tu- 

 bercle with a median notch above. The foramen magnum is a ver- 

 tical ellipse, with lateral processes encroaching upon it, as in Didus ; 

 but in this large extinct bird the upper half of the foramen is nar- 

 rower and almost pointed above. In Apteryx and Palapteryx the 

 foramen is widest transversely. The margin of the foramen magnum 

 is broad and excavated in both Dinornis, Otis and Didus, but the 

 upper border ends in the latter genus in a tubercle on each side. 



In Didus there is a small middle supraoccipital foramen and two 

 lateral ones, but these do not exist in Dinornis, Otis, or Palapteryx : 

 the lateral foramina are present in Apteryx. 



In the extinct genera and in Otis the supraoccipital ridge is well- 

 marked, but defined rather by the subsidence of the occipital surface 

 than the elevation of the ridge above the parietal one. 



In no bird is the extent of surface for muscular attachment so great 

 at the back part of the head, or so strongly marked by depressions 

 and ridges, as in the Dinornis. 



The extension of the surface by the downward thick wedge-shaped 

 development of the basi-occipito-sphenoidal surface, and by its lateral 

 strong backwardly produced ridges, is quite peculiar to the Dinornis, 

 An approach to this structure is made by Otis in the ridges that con- 

 nect the sides of the flat basisphenoid* with the paroccipital * pro- 

 cesses. In Palapteryx the basi-sphenoid is square and flat below, in 

 Didus it presents a longitudinal channel bounded by parallel lateral 

 ridges ; the sides of the basisphenoid, which incline to these ridges, 

 are slightly concave, have two perforations posteriorly, one above 

 and a little in advance of the other, and form the anterior and internal 

 boundary of the tympanic cavity. 



In Palapteryx, as in Didus, the basioccipital descends and expands 

 into two thick obtuse processes, from which muscles pass to the in- 

 wardly-bent angles of the jaw. Internal to these processes are two 

 short tubercles. On each side the base of the occipital condyle in 

 Dinornis are three small foramina ; in Didus two, the outer one the 

 largest. 



In DinorniSf Otis and Didus, two foramina, the upper one for the 

 hypoglossal nerve, the lower one for the entocarotid artery, open ex- 

 ternally in a deep elliptic depression. The paroccipital is enormously 

 developed in Dinornis, and sends a rough thick process from its under 

 part to abut against the lateral basioccipital ridge, where it articu- 

 lates and sometimes anchyloses with the stylohyal : in Palapteryx 

 and Didus the paroccipital carries the posterior surface of the skull 

 downwards and outwards in a minor degree than in Dinornis, and 

 terminates in a curved convex thick border : its internal surface next 



* For the definition of these and other anatomical terms the author referred to 

 his ' Report on the Homologies of the Vertebrate Skeleton ' in '• Report of British 

 Association, 1816." . 



