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GENERAL ORNITHOLOGY. 



Fig. 67. — The post-oral arches of the 

 house martin, at miihlle of period of ineuha- 

 tion, lateral view, X 1-1 diameters- w?/,-, stump 



the exoccipital {teo). This trowel of cartilage is the upper anterior segment of the hyoidean 

 (second post-oral) arch, being to that arch what the pterygo-palatiuo bar is to the mandibular 

 (first post-oral) arch. Several parts of this stapedial cartilage are recognized, as named in the 



fine print under the figure. If the connections of the 

 second post-oral arch were completed, as those of the 

 first are, the tongue bone would be slung to the skull 

 as the lower jaw is ; Ijut they are not, the tract I'ep- 

 resented by the dot-line from the atylo-hyal, sth, to 

 the cerato-h;/al, cliij, being, like ist, above sth, only 

 soft connective tissue. This defect of connection is 

 made up for by the great development of the hyoidean 

 parts of the third post-oral arch, hr 1 and hr 2, which 

 retain the tongue-bone in position, without however 

 articulating it with the .skull. The hand of the trowel 

 of cartilage soon segments itself off from the ear-cap- 

 sule, bringing away with it a small oval piece of the 

 periotic wall, which piece is the true stapes, and the 

 oval space in which it fits is the fenestra oralis leading 

 of meckeli.an or maudibuiar rod, its articular j^^-g |i^„ inmost ear (the cocliUa). The broad part of 

 part, ar, already sliapen ; fy, quadrate hone, or i-iii-i t. i i., 



the trowel-blade is the extra-stapedial part, on which 



the meinhrana tijiiipani, or ear-drum, will be stretched. 



The stylo-hyal, sth, will join the extra-stapedial 



plate, and the afterward chondritied band of union will 



be the infra- stapedial, ist. (Figs. 71, .s*, and 83.) 

 Keturniug „, ~'"fv_<?^ p 



now to the ' {\^ 



chick's head, <=^ / fj) 



which we left ' '^^ ~ 



to examine 



the intricate 



ear - parts at 



the proximal 

 end of the second post-oral arch, we see by fig. 68 

 how rapidly the parts are shaping themselves at the 

 end of this second stage of development. This figure 

 shows the cartilaginous skull, in which no trace of 

 ossification has apipeared, excepting in the under 

 inaudible. The brain and membranous parts of the 

 craniuir. have been removed. The roof of the skull 

 never becomes cartilaginous, bone there growing di- 

 rectly from the membrane ; and the whole of the chon- 

 dro-cranium, as shown in the figure, is one continuous 

 cartilaginous structure (like the whole skull of an 

 adult shark or skate), excepting the parts of the post- 

 oral arches, which are separate. The auditory cap- 

 sule is environed by occipital cartilage, eo, stretch hig 

 over the back of the skull, and by wing-like growtlis 

 {alisplienoids, as) which wall most of the brain-box 

 in front. The high orbito-nasal septun 



suspensorium of lower .jaw, ■ivitli a free anterior 

 orbital process and long posterior otic process 

 articulatint^ with the ear-capsule, of which teo, 

 tympanic wing of occipital, is a part ; mt;i. 

 (■st, .s',s^ tfil, .s/ft, parts of the susiiensorium of 

 the third post-oral arch, not completed to chij ; 

 77is^, juedio-stapediid, to come away from teo, 

 bringing a piece with it, the true stapes or co- 

 lumclt"- aiirls', the oval base of the stapes fit- 

 ting into the future fenealra ovalis, or oval 

 window looking into the cochlea ; sst, supra-sta- 

 pedial ; est, extra-stapedial ; tst, infra-stapedial, 

 w^bich will unite with stir, the stylo-byal ; 

 c?iy and bhy, cerato-hyal and basi-hyal, distal 

 parts of the same arch ; hbr, hr 1, br 2, hasi- 

 branchial. epi-branchial and cerato-branchial 

 pieces of the third arch, composing the rest of 

 the hyoid bone ; ^t/, tongue. (After Parker.) 



Fig. 68. —Skull of chick, second stage, in 

 profile, brain and membranes removed to 

 show cartilaginous formations, X 4 diameters. 

 eth, ethmoid, forming median nose-parts and 

 inter-orbital septum ; developing later.al parts, 

 as ate, aliethmoid, als, aliseptum, atn, alinasal, 

 jwp, partition between nose and eye: p7i,\ire- 

 nasal cartilage ; ps, presphenoidal part of nnd- 

 ethmoid : 2, optic foramen; as, alisphenoid, 

 walling brain-box in front ; pf, jiost-frontal, 

 bounding orbit behind; pa,pg, palatine and 

 pterygoid; </, quadrate; so, supra-occipital; 

 CO, cx-occipital ; oc, occipital condyle, borne 

 upon basi-occipital, and showing ytc, remains 

 of notochord ; these occipitals bound the fora- 

 men magnum, .and eo expands laterally to form 

 a tympanic wing, circumscribing the external 

 auditory orifice behind and below; hsc,psc, 

 horizontal and posterior vertical semicircular 

 canals of ear,- /r, st, fenestra rotunda and 

 fenestra ovalis, leading into inner ear, lat- 

 ter closed by foot of the st.apes .- ?»/,-, ch, bh, 

 bt)r, ct>r, chr, parts of jaw and tongue, as nam- 

 ed ill figs. 65, 66 and 67, (After Parker.) 



is a continuous vertical plate of cartilage, upgrovv'ing 



from the tract of the conjoined trabecular. Lateral developments of this ethmoidal wall, in 



