No. I.] THE VERTEBRATE EAR. 337 



EXPLANATION OF PLATE I. 



Fig. I. The left internal ear oi Dasyatis centrums, seen from the outside, slightly 

 enlarged, x., the utricular canal or appendix from which the anterior and external 

 canals are given off. Opposite the letter the channel of communication, z., the sac- 

 cular appendix and connecting canal. The connecting canals are not symmetrically 

 placed with reference to the endolymphatic duct, ab., nerve of the abortive canal 

 organ which lies in z. r.L, lagena nerve; r.s., saccular nerve, etc. The lagena and 

 post, ampulla appear in the figure in contact. They are separated by a considerable 

 space, which here disappears in perspective. Osmic acid preparation. 



Fig. 2. The right internal ear of Carcharias litioralis, seen from below and out- 

 side, to show the distribution of the nerves. Natural size. The cartilaginous case is 

 partly dissected away, but sufficient remains to illustrate the relation of the mem- 

 branous ear to the supporting structure. The relative sizes of the ear canals and the 

 channels in the cartilage are clearly shown. Osmic acid preparation. 



Fig. 3. The left ear of Torpedo occidentalism seen from below and outside, show- 

 ing the nerve distribution. The dorsal portions of the ear are not represented, and 

 only part of the nerve end organs. Natural size. The splitting of the saccular nerve 

 into two parts, one of which supplies the lagenar organ, is shown. Osmic acid prep- 

 aration. 



Fig. 4. A view from below of the nerve supply of the ear of Petromyzon niarinus 

 in its main branches, g VIII -1- ac, the auditory ganglion with which the accessory 

 nerve is closely connected; r.p. and r.a., the posterior and anterior branches of the 

 so-called auditory with their two main branches, r.a.c. VIII, the accessory branch 

 of the facial supplying the facial sense organ and the epithelial walls of the ear. The 

 VII nerve appears in the figure to lie upon the VIII and its ganglion, but in reality 

 lies between the observer and the VIII, and only traverses the auditory capsule. 



Fig. 5. A sketch of the apparent origin and cranial exit of the V, VII, VIII, IX, 

 and X nerves of Carcharias littoralis from the right side, seen from within. The 

 brain has been raised and displaced to the left, so that only the ventral border of it is 

 visible. The peripheral approach of the acustico-facial and the glossopharyngeal 

 trunks is apparent even within the cranial wall. 



Fig. 6. A very young embryo of Acaiithias vulgaris, seen from the right side, 

 illustrating the early appearance of the auditory saucer. The relation of the auditory 

 sensory thickening to the remaining superficial sense organs is not here shown. X 20, 



Fig. 7. Two figures of the internal ear of a 2.5 cm. embryo, Galeus canis. X 30. 

 The ear sacs are compressed laterally. The separation of the sense organs is in 

 progress, and all their important canal chambers are indicated at this early stage. 



Fig. 8. Internal ear of a 2.5 cm. Galeus canis embryo, to illustrate the formation 

 of the canals. X 35. The stage of development shown in this figure precedes by a 

 short time the condition shown in Fig. 7, and the endolymphatic duct is relatively 

 larger. 



Fig. 9. Sketch of the internal ear of the left side of a 63-day Salmo fario 

 embryo, to illustrate the manner of the formation of the semicircular canals, after 

 von Noorden. The elliptical folds are about to fuse, thus completing the primary 

 arch over the sense organs of the ampullze. The latter are well-formed hills of hair- 

 bearing sensory epithelium before they are thus inclosed, c, otoliths, of which there 

 are two groups of small and one large one present. 



Fig. 10. Sketch cf the nerve branches of the ramus anterior of the auditory 



