122 MR. W. K. PAEKER ON THE STEUCTUEE AND 



miscalled " the maxillary process of the first visceral arch," and just as Meckel's cartilage 

 is the pith of the mandibular arch. 



We saw that the second prestomal rod had become inferior, morphologicaUy, to the 

 first poststomal : a still further degradation takes place in the intermaxillary, that is, in 

 its primordial parts ; for in the bird the rods coalesce throughout their whole length, 

 whilst the plane of the rods is coincident with that of the cranio-facial axis, of which 

 they, from lack of segmentation, are a mere forward continuation. At this stage 

 (Struthio, " A.") these confluent rods (Plate VII. figs. 1-5, p.n.) are at their fullest 

 development ; afterwards, all that part which is free of the nasal passages anteriorly, 

 gradually shrinks, is very small at the time of hatching, and eventually disappears. 

 The foremost two-thirds of Meckel's cartilages undergo the same wasting ; but this 

 decadence is not seen in any part of the palatine rod, at least in the Ostrich : in some 

 birds, e. g., the Psittacinse, the palatines become premorse anteriorly. But this is in the 

 osseous stage, which the prenasal and Meckelian cartilages never attain to, being merely 

 temporary structures. 



That part of the premaxillary pith which does continue in the Ostrich, is ossified 

 continuously with the perpendicular ethmoid : this is extremely unlike what obtains 

 in the higher birds, where the vestibular or sifting portion of the nasal structures, and 

 the axis of the intermaxillary structures, become wholly segmented from the skull and 

 from that part of the nasal capsule which is supplied with the olfactory filaments, and 

 which gives origin to the palatine pedicel. An exorbitant development of the anterior 

 intermaxillary splints is characteristic of birds, but in Struthio, and most of its con- 

 geners, it is the vomer which attains to the greatest relative size. There may be four 

 pairs of intermaxillary splints ; but in the Ostrich the essentially double vomer (Plate 

 VII. fig. 4, V.) is only split at each end — it is an azygous piece ; this is the inferior 

 and posterior splint, and is apt to run far backwards into the palatine region, sheathing 

 the coalesced trabecular beam anteriorly, and the rostrum of the basisphenoid behind. 



In the Ostrich, as in all birds, the intermaxillaries (Plate VII. p.x.) themselves are 

 always symmetrical; but their separateness is extremely transitory; they commence 

 upon the sides of the upper surface of the depressed end of the prenasal rostrum — their 

 proper pith of cartilage. Each piece is composed of a body, from which proceed the 

 nasal (Plate VII. fig. 5,p.x.), angular (Plate VII. fig. 3, p.x.), and palatine (Plate VII. 

 fig. 4, P-X-) processes. 



The dentary margin of the body of these bones meets the palatine processes at an 

 acute angle ; in the Mammal this space is the anterior half of the " anterior palatine 

 foramen ;" it is filled up in the bird on each side by the anterior pointed end of the 

 middle intermaxillary splint. These bones, the " prevomers " (Plate VII. figs. 3 & 4:,p.v.) 

 have been much misunderstood, being mistaken in the bird for the true maxillaries, and 

 in the Ophidians, Lacertians, and Amphibians for the inferior turbinals. 



Already in Struthio, " A.," they have almost attained their proper form, and each 



