104 MR. W. K. PARKER ON THE STRUCTURE 



growth from the two sides (see fig. 4), when these masses are approximating below the 

 coalesced trabecular. 



Before dismissing the chick's skull I have to speak of the posterior conjugational pro- 

 cesses connecting the trabecular with the next facial bar, the pterygo-palatine. 



These parts, the basipterygoids with their articular plate and the corresponding 

 structures in the pterygoids, are thoroughly worked out in my paper on the " Fowl's 

 Skull" (plate lxxxiii. p. 781) ; but the general morphology, their symmorphism with the 

 anterior conjugationals of the same arch, was not clearly seen. 



Before closing this supplemental description of the fowl's skull, I may remark that 

 the fenestra which severs the perpendicular ethmoid from the nasal septum (" Fowl's 

 Skull," plate lxxxiii. fig. 4, c.f.c) is the redifferentiation of the trabecular from their 

 surroundings. 



In many birds another fenestra, besides the " hinge " and the interorbital space, is 

 found in the nasal septum; and in the Goose tribe a fourth appears between the upper 

 turbinals ; to this is added, in Pelecanoides urinatrix, or Petrel, a fifth large fenestra, 

 close behind the antorbitals. 



In the adult Swift ( Gypselus apus) there are four membranous fenestras in the inter- 

 orbital space, instead of two as in JPelecanoides, and one as in Birds generally. This 

 gradual fretting-away of growth-tracts which at one stage of metamorphosis obscure 

 essentially distinct parts is of extreme interest ; the highest and, as it were, the imago 

 forms show this most, notwithstanding that they use up and mix together in many ways 

 parts that remain thoroughly distinct in types that may be compared to the pupce and 

 larvce. As the two preoral arches are intimately interblended, not only with each other 

 but also with the nasal labyrinth and the cranium, it may be well to set down fairly what 

 splints or secondary bones become applied to or grafted on these arches. 



To the hinder pan, the " palato-pterygoids," secondary developments of the mandible 

 or first postoral, there belong the maxillaries, palato-maxillaries, interpalatines, jugals, 

 and quadrato-jugals. 



The trabecular arch draws to itself, as subcutaneous or submucous bones, the follow- 

 ing — namely, the premaxillaries, septo-maxillaries, vomer or vomers, and the para- 

 sphenoid ; the " os uncinatum " is an endosteal part. 



The splints of the mandibular arch were described in my former paper. The tympanic 

 chain of the Bird is a masked splint-series to the segmented and metamorphosed apex of 

 the hyoid arch. 



On the Structure and Development of the Facial Arches in the Passerine types, 

 " Coracomorphse " (Huxley). 

 In the paper already referred to, Professor Huxley has sought to group the flying 

 birds in accordance with the spirit of Humboldt's plant-groups in his ' Views of Nature.' 

 The group under notice, then, is his " Coracomorphse," or Crow form (p. 469) ; this is 

 bo large that (as my friend Mr. Osbert Salvin informs me) whilst the birds already known 

 and described are about ten thousand, half, or well nigh half, of them belong to this one 

 group. Now the type the skull of which I have already worked out, namely that of 



