DEVELOPMENT OF THE SKULL IN THE OSTRICH TRIBE. 151 



its dilated end. In the bird the cranial cavity is aborted anteriorly by the upgrowth of 

 the gi-eat interorbital septum ; the crista galli underprops the frontals directly, and the 

 posterior end of the middle ethmoid (above) goes far back to join the presphenoid. On 

 the latter the olfactory crura rest ; the sides of the former (the supero-posterior part of 

 the middle ethmoid) are grooved to lodge them as they pass mesiad of, and over the 

 large eyeballs to reach their destination. The posterior margin of the pars plana is thick 

 and turned inwards, and stands upwards and a little backwards ; nearly all its inner sur- 

 face is occupied with an ovoidal tent-like outgrowth (Plate XII. fig. 7, m.t.b., a bristle 

 is passed into the opening), which is bifurcate a little below, and which, for the lower 

 half of its anterior margin, is not confluent'with the primary 'cartilage ; this slit there- 

 fore opens into the deep crescentic groove which separates the upper from the middle 

 turbinal. These two swellings lie near together, and the posterior end of the lower tur- 

 binal passes equally downwards and backwards beneath them (Plate XII. fig. 7, i.t.b.). 

 This lower turbinal is not at all simple ; it is complex beyond expectation. 



As soon as the primary septal ala (continuous with the ethmoidal) begins to turn 

 inwards, it becomes double (Plate XII. fig. 9, al.s., i.t.b.), one lamina keeping the sigmoid 

 curve of the upper turbinal, the other growing downwards, and then first outwards and 

 afterwards inwards, to form the outer nasal wall ; when it is nearly halfway down it gives 

 off, from its outside, a small lamella which is connected by a fascia with the edge of the 

 upper jaw. This fascia halfway down gives off a horizontal lamella (Plate XII. fig. 9), 

 which joins the cartilaginous wall within ; the cartilaginous plate nearly reaches the base 

 of the septum nasi (s.n.), it becomes the ala nasi anteriorly. The inner sigmoid lamella 

 (Plate XII. fig. 9, i.t.b.), which towards the septum is first convex, then concave, and 

 then convex again, gives off truly cartilaginous secondary lamellae, four of which bifur- 

 cate again, whilst five continue simple ; so that in all there are no less than thirteen free 

 plates. Behind, this great inferior turbinal becomes simpler (Plate XII. figs. 7 & 8, 

 i.t.b.), and this part is seen from below roofing the middle nasal passage (Plate XL fig. 2, 

 i.t.b.) ; in front it does the same, and ends at the middle of the true ala nasi; this latter 

 cartilage (Plate XI. fig. 3, al.n.) has no independent outgrowths of its own ; it is very 

 large and simple, and ends in a crescentic manner over the oblique anterior nasal 

 opening. The somewhat thin nasal septum (Plate XII. fig. 9, s.n.) is one continuous 

 sheet of smooth cartilage, and at first almost entirely fills up the space below the nasal 

 processes of the intermaxillaries, to their solid part in front ; afterwards, when ossified, 

 it will be relatively much smaller. The manner in which the lacrymal embraces the 

 lateral ethmoidal structures at every available point of contact (Plate XII. fig. 8, L), 

 shows its true nature as the protective " operculum " of this region ; a band of cartilage, 

 which becomes thicker-edged below, lines the front of the antorbital plate of the lacry- 

 mal almost to its edge ; it is the lower and posterior part of the inferior turbinal (a.i.t.), 

 and is often in higher birds an autogenous cartilage, to be afterwards separately ossified ; 

 and there is nothing in the bird's skull more curious than this lower " antorbital," which 

 in certain species so closely imitates the " transpalatine " of the Keptile. 



