6 MR. W. K. PARKER ON THE MORPHOLOGY OF 



and only partly redivided by this same interorbital window. Here turns up the ex- 

 planation as to why the anterior sphenoid (p.s) should be perched up high above the 

 ethmoidal and basisphenoidal base-line. This part, with its arrested " or bito- sphenoidal " 

 lips, is at present unossified ; it has, afterwards at least, three centres — one for the body, 

 and a large pair for the wings ; and it ends above in the peaked extremity of the frontal 

 region of the mesoethmoid (m.eth). This latter region is very large ; but its lower half 

 is borrowed territory, belonging to the subjacent portion of the long trabecular com- 

 missure with its ascending crest ; four fifths of this composite plate is already ossified, 

 about to become the largest mesoethmoid (relatively) in the vertebrate series : I speak 

 of that of Birds generally. In the adult the double nasal sac is separated for the most 

 part by the merest film of membrane (Plate II. fig. 5, c.f.n) : this fenestrate space has com- 

 menced as a " notch " by the absorption of part of the trabecular tract (Plate I. fig. 3 

 c.f.n), both base and crest. This is the beginning of the notch which at once divides 

 the first facial arch into a proximal and a distal portion, and also separates the middle 

 wall of the nasal labyrinth into a vestibular and a true sensory region. The septum nasi 

 (s. n) is a thinnish continuous plate of cartilage, terminated by the stunted prsenasal 

 above, and by the thick projecting trabecular cornua below (fig. 3, p.n, c.tr). An outer 

 side view of the same part of the face (fig. 4) shows that the great median ethmoidal 

 ossification (" pars perpendicularis ") is growing outwards into the alee, or upper part of 

 the " ectoethmoid," whilst the lower part ("pars plana") has its own ossification 

 (p.e,p.p). 



The angle below the centre for the pars plana is the substratum that should form the 

 " os uncinatum;" the mass in front of this part, and below the superior turbinal (u. tb), 

 is the nasal gland (n.g) ; the " aliseptal" (al.s), or root of the inferior turbinal, is seen 

 above; in front of this the " alinasal" fold (al.ri) ; below this the nasal floor (n.f), and 

 altogether in front the pedate trabecular cornu (c. tr). All these parts are brought into 

 daylight by transverse sections (Plate I. figs. 5-8). In the foremost of these (fig. 5) the 

 recurrent trabecular horns (c. tr) are shown as two thick lobular masses of cartilage, with 

 a binding isthmus formed between the ends of the " cornua." This is very similar to 

 what is seen in an ordinary Mammal, e.g. the Pig. Hedging in the tuberous mass we 

 see the nasal processes of the prsemaxillaries (n. px), the dentary part (d.px), the fore 

 shaft of the maxillary (mx), the palatine spur of the prsemaxillary {p. px), and outside 

 this the prsepalatine bar {p. pa). In the next section (fig. 6) the same bony sections are 

 shown, with the exception of the palatine portion of the prsemaxillary. The " nasal 

 nerves " (n. n) come into view here below the fore part of the septum (s. n), and at the top 

 this wall has grown into a pair of roof-plates (aliseptals), which develop into a large 

 thick half-scroll, the " alinasal turbinal " {at. tb). Outside these valvular growths 

 there is an infero-lateral development of cartilage, which at first is a wall and then a floor 

 (n. id, n.f). In the succeeding section (fig. 7) new parts come into view : the two arms 

 of the nasal bone (n) ; the interpalatine spur (i.pa) ; and the fore part of the " inferior 

 turbinal " (*. tb). The section of this arrested scroll is hammer-shaped, an outgrowth 

 being developed inside as well as outside the root ; the outer coil is the rudiment of the 

 scroll, which in Rhea and Tinamus is coiled upon itself three times (" Ostrich skull," 



