144 MR. W. K. PARKER ON THE STRUCTURE 



cloth which is thrown over the brain-sac in the Salmon and Polypterm (see my memoir 

 on the " Salmon's Skull," Phil. Trans. 1873, plate v. t.cr), the tegmen cranii. 



The reason for the membranous space between the eyes is not primarily teleological. 

 Nature is not husbanding her cartilage as being poor in that substance ; it is a secondary 

 cleft, tending to divide the overlying ethmoidal structures from the crest developed on 

 the coalesced trabecular. 



The roofing bones are seen to be well developed, the frontals, parietals, and squamosals 

 (f,p,sq); the latter are elegant sub falcate bones, running far along the postorbital part 

 of the frontals, and somewhat trilobate below, where they clamp the ear-capsule. The 

 columella (st) is ossified in its medio-stapedial region, and the quadrate also, not its pedicle 

 or orbital process ; its otic facets and its double lower condyles are all soft as yet. 



In this stage I have only brought into view the hinder facial parts ; the pterygoid (pg) 

 has now a long splint-like process which reaches to the corresponding crus of the vomer, 

 not here shown, but seen in fig. 12, v *. 



Afterwards the absorbents fret a suture across the base of this spur, and convert it into 

 a separate mesopterygoid, which, however, is only distinct for a few weeks, for it soon 

 coalesces with the postero-superior edge of the palatine. 



The relation of the jugal to the quadrato-jugal, and of the latter to the quadrate, into 

 which its hooked end is inserted, is here shown (fig. l,j, qj, q). 



The long dentary, which has coalesced with its fellow at the "mentum," has been 

 removed, but the proximal part of the free mandible is shown (fig. 4, outside ; fig. 5, 

 inside). 



Meckel's cartilage (mk) is still large, and runs far forwards ; its articular end, with its 

 short Pluvialine posterior and internal angular processes (pag, lag), is ossifying ; there is 

 an endosteal patch and a long ectosteal plate (ar). 



I see no separate coronoid, a bone often indistinct in birds ; but the splenial, angular, 

 and surangular (sp, ag, sag) are large and still free. 



In these long-faced birds the glossal portions of the hyoid are more than their hypo- 

 hyals ; they deserve the name here of cerato-hyals (fig. 6, chy) ; they are unossified and 

 confluent. 



There is a common cartilaginous basibranchial element (bbr), pointed and delicate 

 behind, and only the proximal part of the first branchial arch (thyro-hyals, brs) is 

 ossified ; the dorsal element is long, slender, and soft. 



The nasal cartilages have been cut away and turned on their dorsal face to show their 

 laminar outgrowths (fig. 7) ; the section was made close behind the hinge or notch (see 

 fig. 1), and a line in front of the meso-ethmoidal bony centre (pe). 



Unlike what we see in Mammals, the turbinal that figures most largely here is that 

 belonging to the alse nasi. This alinasal turbinal (atb) is here a simple foliaceous 

 outgrowth (see it in section, fig. 8). Behind this, and rising above it, is the inferior tur- 

 binal (itb). This is a simple plate at its commencement ; further back it is coiled upon 

 itself. In most birds this scroll has two coils. 



* This is a primordial relation of the pterygoid and the vomer; it is found in the lowest Urodela, to say nothing 

 of the Rh vnchosauria. See Huxley, Proe. Zool. Soc. 1874, pi. xxix., and Giinther, Phil. Trans. 1867, pi. i. fig. 2. 



