MR. W. K. PARKER ON THE OSTEOLOGY OF BAL^NICEPS REX. 315 



and lower margin, where it has contracted adhesion with the sur-angular and angular 

 pieces : here it is lozenge-shaped, whilst in the Jabiru it is reniform. 



The development and condition of the coronoid in the Adjutant is very much like 

 what obtains in the Heron ; the Albatros also has the same element large, and although 

 bony union has taken place between it and the sur-angular above, as also with the 

 articular and angular behind and below, yet its outline is easily traced. In Cranes 

 and Geese the thin splint-like oblique ' coronoid ' is either connate, or has coalesced with 

 the ' articular ' behind. In Grus americana there is an oblong membranous space ante- 

 rior to the inferior dental foramen ; in the Rook this space is oval, and is behind that 

 passage ; Passerine birds and Owls have a similar structure, but the Diurnal rapacious 

 birds have a stronger and more completely ossified mandible. In the Little Goatsucker, 

 Caprimulgus europaus, the articular moiety of the lower jaw is thick and cellular, compared 

 with the dentary ; it has no membranous part, and being curiously bowed outwards, 

 the dental foramen enters it on the lower margin. Such modifications (which are end- 

 less, and in each case beautifully adapted to the life of the bird) are here mentioned 

 only to show that the massive development of the mandible of the Balasniceps is to a 

 great extent teleological. The embryological researches of Reichert and Rathke have 

 proved that the articular element of the Bird's mandible is the ossified proximal end of 

 Meckel's cartilage, and is the homologue of the ' malleus ' of Mammals : see Professor 

 Huxley's Croonian Lect. p. 16. 



Development of the Mandible. 



We must refer the reader to the excellent writings of Professors Goodsir and Huxley 

 for an account of the morphological meaning of the mandible in birds and in vertebrates 

 generally ; the views of the former author will be found in the papers so often referred 

 to (p. 173), and those of the latter in the Croonian Lecture (p. IG). 



It must, however, be borne in mind that the mandible belongs to the same sclerotome 

 as the squamosal and petrosal. Meckel's cartilage has attained its largest development 

 in the Chick by the eleventh day of incubation, but it has become separate from its 

 fellow of the opposite side at the distal end. The proximal cartilage (the 'quadrate') 

 of this, the first proper facial arch, has begun to ossify in its thickest part at this time, 

 but the ' articular ' (or ' malleal ') portion is entirely cartilaginous. The dentary 

 elements are not only ossified, but, getting the start of the pre-maxillaries, they have 

 become fused together at the symphysis. The angular and sur-angular pieces are also 

 ossified ; but the 'splenial' is still membranous ; and there is no ' coronoid ' in the Fowl. 

 All the mandibular elements except the articular are formed (like the pre-maxillaries) 

 in perichondrial membrane. From the fourteenth to the nineteenth day the cartilages 

 of Meckel are seen to be wasting fast, just as the ethmo-vomerine process for the pre- 

 maxillaries does. At the end of the second week of incubation the ' splenial ' element is 

 ossified, and there is a small square osseous centre in the thick ' articular' portion oi 



