. Text book of vertebrate zoology. Vertebrates; Anatomy, Comparative. l6o -MORPHOLOGY OF THE ORGAXS OF jaw of the adult is without a quadrate suspensorium. In the €mbr\-o mammal, however (Fig. 169), ^Meckel's cartilage is seen to be connected to the otic capsule by means of a quadrate, from which a stapedial process extends backwards to articulate with the outer end of the stapes, in a manner which strikingly recalls the relations in the urodeles. The proximal end of Meckel's cartilage is expanded, and, besides articulating with the quadrate, sends a long process, the future manu
. Text book of vertebrate zoology. Vertebrates; Anatomy, Comparative. l6o -MORPHOLOGY OF THE ORGAXS OF jaw of the adult is without a quadrate suspensorium. In the €mbr\-o mammal, however (Fig. 169), ^Meckel's cartilage is seen to be connected to the otic capsule by means of a quadrate, from which a stapedial process extends backwards to articulate with the outer end of the stapes, in a manner which strikingly recalls the relations in the urodeles. The proximal end of Meckel's cartilage is expanded, and, besides articulating with the quadrate, sends a long process, the future manubrium, back- wards and inwards, be- tween the t}'mpanum and the external auditor}- me- atus, /. e., into the tym- panic membrane. Later, with the formation of membrane bone (dentary) around the more distal portion of Meckel's car- tilage, the lower jaw ac- FiG. 169. Diagram of auditory ossicles and ^ related parts in the mammalia, based on the with the skull, On the embryo rat. a, external auditory meatus; ct, under Surface of the Zy- chorda tympani; / facial nerve ;^, hyoid; h,n, ^j^ ^^^^^ ^j^jj^ ^^ Jiyomandibular nerve ; hn, hyoid branch of faci- ° ^ alis; /«, mallear portion of Meckel's cartilage, its the Same time the prox- process extending down between tympanum and imal end of ^leckel's car- meatus; mn, mandibular branch of facialis; tilage bccOmCS Segmented ^ \i), quadrate, later mcus; s, stapes; sm, sta- ° pedial muscle; /, tympanum. off from the rest, and gives rise to the malleus. The quadrate, having no longer to sene as a suspensorium, loses its connection with the otic capsule, and becomes the incus. Incus and malleus extend into the tympanic cavity from in front, , are prespiracular, and cannot be homologous with the anuran and sauropsidan columella. Further, it will be noticed that the ossicula of the mammal are on the oppo- site side of the chorda tympani from what is found in the rep- tilia (Fig. 168). It is an interesting fact, the bearings of which w
Size: 1828px × 1367px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, bookpublishernewyorkhholtandcom
