FORMATION OF THE AUDITORY OSSICLES. 



167 



JVSt.C/i 



Fig. 198, A. ELEMENTS OP THE SKULL OF AN EMBRYO PIG, |-INCH LONG, VIEWED FROM BELOW : 

 SEMIDIAGRAMMATIC. (From Balfour after Parker.) 



pa.ch, parachordals ; nc, notochord ; au, otic capsule ; py, pituitary ; tr, trabeculse ; c.tr, cornu 

 of the trabecuia ; pn, prenasal cartilage; e.n, external nares ; ol, olfactory region ; p.pg, palato- 

 pterygoid bar enclosed in the maxillo-pterygoid process ; mn, mandibular bar ; hy, byoidean bar ; th.h, 

 thyrohyoid bar ; 7a, aperture for facial nerve ; 8a, for glossopharyngeal ; 86, for vagus ; 9, for hypoglossal. 



Fig. 198, B. SIDE VIEW OF THE MANDIBULAR AND HYOID ARCHES IN AN EMBRYO PIG OF 1| INCH 

 ; IN LENGTH. (From Balfour, after Parker. ) 



tg, tongue ; mk, Meckel's cartilage ; ml, body of malleus ; mb, its manubrium or handle ; t.ty, 

 tegmen tympani ; i, incus ; st, stapes ; i.hy, inter-hyal ligament ; st.h, stylo-hyal cartilage : h. k, 

 hypohyal ; bh basibranchial ; th. h, rudiment of first branchial arch ; 7, facial nerve. 





JfateZ! 



M 



THE EMBRYO OF THE SHEEP. (Salensky. ) 



pears, or in some animals may not 

 be found at all. This bar is in 

 all cases of less importance than 

 the first two, from the proximal 

 parts of which important struc- 

 tures connected in lower verte- 

 brates with the suspensory appa- 

 ratus of the lower jaw, in the 

 higher vertebrates with the ap- 

 paratus for sound transmission 

 to the internal ear are developed. 

 Formation of the auditory 

 ossicles. If the embryonic de- 

 velopment of the bars is studied 

 in man and other mammals, it is 

 found that at a certain period of 

 foetal life Meckel's cartilage is 

 directly continuous with the car- 

 tilaginous malleus, above which, 

 and at first in direct continuity 

 with it, is the cartilaginous incus 

 (fig. 199) ; these two ossicles 

 therefore appear as the enlarged 

 and modified proximal end of 

 Meckel's cartilage. Somewhat 

 later the incus becomes detached 

 from the malleus, but the latter 



errors* STJL, lon s remains in continuit y with 



Meckel's cartilage (fig. 200). 



