154 



GENERAL ORNITHOLOGY. 



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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-palatiue bar is to the mandibular 

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



fine print under the figure. If the connections of tlie 

 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 ; but they are not, the tract rep- 

 resented by the dot-line from the stylo-liyal, sth, to 

 the cerato-hyal, cliy, 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, 6r 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 #rom the ear-cap- 

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

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

 oval space in which it fits is the /e«es^ra oraKs leading 

 into the inmost ear (the cochlea). The broad part of 

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

 the memhrana tympani, or ear-drum, will be stretched. 

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

 est, ssf, ist, s?7i, parts of the snst)ensorium of plate, and the afterward chondrified band of union will 

 ^:t^^:S;:S^::^X;Z^':^:^^^'^, ^ei^.ei.^ra-stapedial,ist. (Figs. 71, «^, and 83.) 



Returning ctA^f^^ 



now to the 

 chick's head, 

 wdiich 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 appeared, excepting in the under 

 mandible. The brain and membranous parts of the 

 <'.ranium have been removed. The roof of the skull 

 never becomes cartilaginous, bone there growing di- 

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

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

 cartilaginous structure (like the whole skuU 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, stretching 

 over the back of the skuU, and by wing-like growths 

 (alisphenoidSj as) which wall most of the brain-box 

 in front. The high orbito-nasal septum is a continuous vertical plate of cartilage, upgrowdng 

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



Fifi. 67. — Tlie post-nral .arclies of the 

 house martin, at middle of period of incuba- 

 tion, lateral view, x 1-1 diameters, ml:, stump 

 of meckelian or mandibular rod, its articular 

 part, at; already shapen ; 7, quadrate bone, or 

 suspensorium of lower jaw, with a free anterior 

 orbital process and long posterior otic process 

 articulating with the ear-capsule, of which teo, 

 tympanic wing of occipital, is a part ; mst 



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

 lumella miris ; the oval base of the stapes fit- 

 ting into the future fenestra oralis, or oval 

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

 pedial ; est. extra-stapedial; is*, infra-stapedial, 

 which will unite with sth, the stylo-hyal ; 

 chy and bhij, cerato-hyal and basi-hyal, distal 

 parts of the same arch ; bbr, br 1, br 2, basi- 

 branchial, epi-branchial and cerato-branchial 

 pieces of the third arch, composing the rest of 

 the hyoid bone; tg, tongue. (After Parker.) 



ZA- w,'-. 



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 lateral parts, 

 as ale, aliethraoid, als, aliseptum, ain, alinasal, 

 pp, partition between nose and eye; pn, pro- 

 nasal cartilage ; ps, presphenoidal part of mid- 

 ethmoid; 2, optic foramen; as, alisphenoid, 

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

 bounding orbit behind; pa,pg, palatine and 

 pterygoid; q, quadrate; so, supra-occipital; 

 eo. ex-occipital; oc, occipital condyle, borne 

 upon basi-occipital, and showing no, 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,- fr, st, fenestra rotunda and 

 fenestra ovalis, leading into inner ear, lat- 

 ter closed by foot of the stapes ; ml; ch, bh, 

 bbr, cbr, ebr, parts of jaw and tongue, as nam- 

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



