300 MR. W. K. PARKER ON THE OSTEOLOGY OF BALvENICEPS REX. 



the Adjutant, the Heron, the Rook, the Goatsucker [Caprimulgus), the Swift (Cypselus), 

 and in various other birds, developed as a distinct centre of bone in the cranio-facial 

 axis. The posterior osseous centre has already been described as the pre-sphenoid ; 

 the anterior element (which in a large number of birds consists principally of persistent 

 cartilage, with a membranous space between it and its successor, the pre-sphenoid) is 

 the true ethmoid, the catacentric centrum of the ethmoidal sclerotome (Goodsir, 

 op. cit. p. 143). Cuvier called the posterior piece the ' ethmo'i'de.' It is evident that 

 the axial parts of two cinctures, one of the cranium and the other of the /nee of the 

 Struthionidae, have been considered to belong merely to one segment of the skull. But 

 evidence is not wanting to show that the large axial mass of bone figured 14 by Professor 

 Owen (Rep. on Archet. fig. 8. p. 190) is developed even in the aberrant Brevipennes 

 from an anterior and a posterior osseous centre. Many years ago we dissected and 

 figured the cranio-facial axis of an Emeu {Drornaius ater) only six weeks old, in which 

 the orbito-sphenoidal region, the antorbitals, and the anterior part of the so-called ' pre- 

 frontal mass' were still cartilaginous. The flat-topped pieces, however (the anterior of 

 ■which props up the ' nasals,' the posterior forming the buttress of the sphenoido- 

 frontals), formed one V-shaped piece of bone, the upper portions being quite distinct, 

 ■whilst the flat descending plates had evidently coalesced ; for ossification commences, 

 not at the point where these pieces had become confluent, but just below the horizontal 

 outspread upper part, where, in this young Emeu, they were still widely distinct. 



Looking at the lower part of the great fronto-maxillary hinge in the Balseniceps, we 

 see, between the incurved plates of the lacrymals, a large mass of thinly-coated spongy 

 bone, ■VN'hich forms the posterior part of the axis of the greatly-developed face. This 

 broad-topped mass of bone acts as a buttress to the nasal processes of the pre-maxillaries 

 and to the nasals, besides forming a large and important part of the ' great hinge,' and 

 articulating with its immediate successor the pre-sphenoid below the hinge, thus adding 

 strength to the junction of the roof-bones. This is the true ' ethmoid' ; at least, it is the 

 homologue of the mesial part of the human ethmoid, the out-standing process of which 

 is called the ' crista-galli.' This centrum of the /ace of Balseniceps is as well developed 

 as its cranial successor the pre-sphenoid ; and the posterior aspect of the former is so 

 much like the anterior aspect of the latter, that it seems like an illusion, and as though 

 a mirror had given us a backward reflexion of the front of the pre-sphenoid. 



The posterior face of the ethmoid of Balseniceps is sharply carinate for about two- 

 thirds of its depth, the keel ceasing and a groove commencing opposite the projecting 

 end of the basi-sphenoid. This groove, very shallow at first, runs downwards until it 

 loses itself between the spur-shaped posterior processes of the ethmoidal pterapophyses 

 in the mesial palatal groove. Where the keel ends, there the ethmoid, the centrum of 

 this sclerotome, has coalesced with its low-lying pterapophyses. The mass of the 

 ethmoid a few lines in front of the keel is much thicker than that of the pre-sphenoid ; 

 but the external bony table begins soon to he deficient on each side, and all trace of 



