ANATOMY OF JURDS 



227 



develops at what will be the end of the upper beak a ])renasal car- 

 tilage, pn, to become the axis of the beak. The mouth is become 

 already better formed, the axis of its cavity pointing more forward 

 than downward ; and great changes are undergoing in parts of the 

 ear at the back corner of the mouth. The quadrate and Meckelian 

 cartilages are assuming much of their true form. The quadrate 

 develops an orbital process which extends free into the orbit, and an 

 otic process which articulates with the auditory sac and parts of the 

 exoccipital cartilage. The rela- 

 tions at this stage have not been 

 made out in the fowl, but are 

 figured and described from the 

 corresponding stage of the Eu- 

 ropean house -martin (Chelidon 

 Mrhica). In Fig. 67, mk is the 

 cvxt stump of the Meckelian carti- 

 lage, of which ar is the articular 

 part ; q is the quadrate, of which 

 a backward process is seen arti- 

 culating Avith teo, the tympanic 

 wing of the exoccipital. Just 

 below and behind this otic pro- 



r. , 1 -I , .-, Fig. 67. — The postoral arches of the house 



cess Ot the quadrate, exactly martin, at middle of period of incubation, la- 



wViPrP in rinpv fml^nrna ie +1ip teral view, x 14 diameters, m/:, stump of Mec- 



wueie 111 lipei eiliuiyub Ih Uie kalian or mandibular rod, its articular part, ar, 



fenestra OValis in which is fitted already shapen -, q, quadrate bone, or suspen- 



, „ „ , . sorium of lower jaw, with a free anterior orbital 



the toot ot the SfajJeS or stirrup- process and long posterior otic process articu- 



bone ot the middle ear, there panic' wing of occipital, is a part ; mst, est, sst, 



appears a trowel-shaped proiec- is«, ^A, parts of the suspeusorium of the third 



^^ 1 1 n f. postoral arch, not completed to chy; mst, 



tlOn of cartilage, the handle of medipstapedial, to come away from teo, brlng- 



1 • 1 . ,. -ii ii ing a piece with it, the true stapes ov colmnella 



wnicn IS continuous with tlie awU ; the oval base of the stapes fitting into 



cnl-iattmr-o nf tlio tity /^nnciilo • tVio the future /oieA'tm ovalis, or oval window look- 



bUUStanct OI t-lie ear-capsuie , tne j^^g j^^^ ^^^ cochlea; sst, suprastapedial ; est, 



sickle-shaped piece behind which extrastapedial ; ist, Infrastapedlal, which will 



. ,1 , • • PI unite with sth, the stylohyal ; chy and bhy, 



IS the tympanic wing OI the ex- ceratohyal and basihyal, distal parts of the 



/-\n«^■1^ifr,^ /f^r,\ Tl i f ,-v 1 /a-P Same arch ; hbr, br I, 6c 2, basibranchial, epi- 



OCCipiCai {leO). XniS tlOWei OI branchial, and ceratobranchial pieces of the 



cartilage is the upper anterior seg- ti^'^i arch, composing the rest of the hyoid 



° • T / T bone ; tQ, tongue. (After Parker.) 



mentof the hyoidean (second post- 

 oral) arch, being to that arch what the pterygo-palatine bar is to the 

 mandibular (first postoral) arch. Several parts of this stapedial 

 cartilage are recognised, as named in the fine print under the figure. 

 If the connections of the second postoral 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 represented by the 

 dot-line from the stylohjal, sth, to tlie ceratohyal, chij, 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 



