NOVKMBER 2. ISS;?.] 



SCIENCE. 



58' 



and can also be made to come out into the 

 tympanum, either through the vestibular or 

 cochlear oijening (fenestra ovalis or fenestra 

 rotunda). In the dr3' skull, either passage is 

 easily made without breaking down, and ap- 

 parently without meeting any bony obstacle. 



If, now, the whole periotic mass be cut awaj- 

 from the rest of the skull with a fine saw, and 

 then divided in any 

 direction, the bony 

 labyrinth and essen- 

 tial organ of hearing 

 can be studied. It is 

 best to make the 

 section in some def- 

 inite plane with re- 

 gard to the axes of 

 the skull, — the ver- 

 tical longitudinal, or 

 vertical transverse, or 

 horizontal, — as the 

 disposition and rela- 

 tions of the contained 

 structures are then 

 more readih* made 

 out. Four or five par- 

 allel cuts will make as 

 many thin flat slices 

 of bone, affording 

 eight or ten surfaces 

 for examination. The 

 whole course of tiie 

 lah^-rinthine struc- 

 tures can be seen in 

 sections, which, put 

 together in the mind's 

 eye, or held in hand a 

 little apart, and visibly 

 threaded with bristles, 

 afford the required 

 picture very nicelj'. 

 At first sight, the 

 unpractised eye will 

 recognize nothing but 

 confusion, — a bewil- 

 dering maze of bone. 

 All this cancellated 

 structure or net-work, 

 however, is pneumat- 

 ic ; tiie open-work tis- 

 sue of l)ono contain- 

 ing air derived from 

 the tympanum, and 

 having nothing to do 



with the auditory cavities proper. P.arts of 

 the bony labyrintli will soon be recognized by 

 their smooth, firm walls and definite courses, 

 as distinguished from tiie irregular interstices 



Fio. 4. — Ripe chick's ekull, loui^itudiiial BecUon 



X 3 diameters. (After I'arker.) In the mandible are seen, — 

 mk. remains of raeciielian rod ; f/, dentary bone ; .v/), splenial ; 

 a, ansrular : *«, surangular ; ai; articular ; ia/>, Internal articular 

 procuse ; pup. posterior articular process : in the skull, — pn. 

 the orii^inat prcnasal cartilage, upon which is moulded the 

 I>reraaxillary, p.r. with its nasal process, npx, and dentary 

 process, ftpj-; an, septo-nas.il cartilage, in which is seen nn, 

 nasal nerve ; ntb. nasal turbinal ; etli. ethmoid ; pe. perpendic- 

 \ilar plate of ethmoid ; iof, inter-orbital foramen : ps. pre- 

 sphenoidat ref^on ; 2, opih- fnramen; as. alisphenoid, with 5, 

 foramen for divisions of the Hflb nerve ;/, frontal ; p, parietal ; 

 «o,supcr-occipital ; ane. superior semicircular canal ; sr, a sinus 

 (venous) canal; fp, cpiotic; eo. exoccipital; op. opisthotic; 

 po, pro-otic, with 7, mfatns auilUoriuH iiilerttun, for entrance 

 of seventh nerve : 8, foramen for vagus nerve ; bo , basi-occipltal ; 

 III, ijasl-temporal ; U:, canal by which carotid artery enters 

 brain-cavity ; up, basi-pteryKoid process; ap to rbn. rostrum of 

 the skull, being the parasplieuold bone underllooring the 

 basl-spbenoid and future perpendicular plate of ethmoid. 



of bone-tissue. They are, as usual, a central 

 vestibular cavity, with its utricular recess ; 

 three semicircular canals ; and the cochlear 

 ca\'it3-, projecting downward like a beak (see 

 figs, i) and 6, the membranous labyrinth, to 

 which the incasing bony cavities closely con- 

 form) . According as the sections have been 

 made, numerous cross-cuts of the canals will 

 be seen here and there 

 as circular orifices ; 

 the canals themselves 

 Ij'ing curled like 

 worms in the petro- 

 sal and occipital sub- 

 stance, their ends con- 

 verging to the central 

 vestibular cavitj'. As 

 compared with those 

 of man, tlie parts are 

 of great size in a bird : 

 in the eagle, for exam- 

 ple, the whole affair is 

 as lai'ge as the end 

 of one's thumb, the 

 whole lengtli of the 

 superior canal is an 

 inch or more, and 

 its calibre, I should 

 judge, is absolutelj' 

 about as great as in 

 man. Tiie cochlea, 

 though not compara- 

 tively diminutive, 

 is in an undeveloped 

 st.ate, as far as com- 

 plexity of structure is 

 concerned, — ligulate 

 or strap-shaped, a lit- 

 tle curved on itself, 

 but making no whorl. 

 This is substantially 

 as in all Sauropsida 

 (birds and reptiles), 

 for the cochlea does 

 not coil into a helix 

 until we reach Mam- 

 malia. Tlie tongue- 

 like alfair is simply as 

 if a part of the first 

 whorl of a niaiiimal's 

 cochlea very incom- 

 pletely divided into 

 scala veslibuli and 

 scaln tympani by car- 

 tilaginous structures representing a modiolus 

 and its lamina, proceeding from the )>ony b.ir 

 or bridge between /ene-s^ra ovalis am\ feriestra 

 rotunda. These are the external (a) and in- 



