DEVELOPMENT OF THE SKULL IN THE OSTRICH TEIBE, 128 



bone may be described as possessing a body, a nasal, an internal or palatine, an external 

 or zygomatic process, and a pedate proximal process, in relation to the sides of the 

 trabecular rod. In Struthio camelics the nasal process is a mere thin and not very broad 

 bridge of bone passing from the proximal to the zygomatic process, on a somewhat 

 higher plane than the body of the bone ; thus making the isthmus between the proximal 

 (internal) part and body of the bone to be double. 



This bone supplies a good instance of the manner in which a splint bone may be 

 formed by the ossification of an aponeurotic tract quite at right angles to and a great 

 distance from the primary rod to which it belongs. All these splints appear to belong 

 to the external category ; if so, only the mandible in the Ostrich-tribe has internal 

 splints. The coalescence of the axial rods makes this apparent difference. 



In Struthio the vomer (Plate VII. fig. 4, v.) has three prongs anteriorly, and is deeply 

 bilobed behind, passing backwards as an under beam, beyond the middle of the basisphe- 

 noidal rostrum in the adult ; in Struthio, A., one-third of the rostrum is thus underlaid. 

 Certainly the formation of the vomer is at first in the outer layer of the perichon- 

 drium which invests all that part of the cranio-facial axis lying in front of the antorbital 

 lamina ("pars plana," "middle turbinal"). The "turbinals" have overshadowed intel- 

 lectually, as they do literally, this matter of the great extent of the primordial part of 

 the intermaxillary apparatus, and the real bearing of its splint-system. Afterwards I 

 will show the fruitfulness of this idea, and how it throws a trail of light along the 

 whole series of " vomers" from their first birth in the Sturgeon to their latest incoming 

 in our own species. The true nature of this splint, the unravelling of the much mis- 

 understood " prevomers," the exact nature of the intermaxillaries proper, and the finding 

 for all these a true embryonic preskeletal basis, is no mean object of ambition. 



The rest of the face is the hyoid arch, with its attached thyrohyals (1st branchial 

 arch (Plate VII. fig. 7). The proximal part of the hyoid arch is the "columella" 

 (stapes) ; it is a mere cylinder of cartilage, which flattens out into an oval disk above, 

 where it serves as an operculum to the fenestra ovalis (fenestra of the vestibule), and is 

 branched below, the thin branches not ossifying. Far removed from this part we find the 

 hyoid cornua on a plane with the base of the skull, and altogether small, and coalesced 

 with each other and with a truly basal piece. The cerato-, basi-, and uro-hyals 

 (Plate VII. fig. 7, c.h.-b.h.-u.h.) are thus already one piece, which is at present totally 

 unossified. These primordial hyoid horns are an exact imitation of an early state of 

 their serial homologues in the first prestomal (intermaxillary) arch (see Huxley's Elem., 

 p, 138, fig. 57, F', rr.). There is much mystery at present hanging over the relation of 

 the cornua of the hyoid to the proximal pieces. Articulating distally with the basal 

 portion of this hyoid cartilage is a rod of cartilage which has another smaller rod arti- 

 culated to it above, which latter ends in a point. These are the thyro-hyals {t.h. 1 & 2), 

 or rudiments of the first branchial arch ; proximally they are free, and curl round behind 

 the occipital cartilage ; none of the lingual cartilages possess any splints, as they do in 

 fishes : the lower thyro-hyal is rapidly ossifying in Struthio, " A." 



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