Anatomical Discoveries respecting [May, 



opened and shut by means of a valve, but forms a muscular 

 tumour, through which the air canal penetrates in a spiral direc- 

 tion, diminished to the fourth part of its size. , V 



19. The ear of the ray fish is not furnished with a single 

 external passage, as all anatomists have hitherto beheved ; but 

 ■with two. Besides the fenestra of the vestibulum cartilagineum 

 closed by a membrane, described by Scarpa and Cuvier, there 

 exists a fenestra of the vestibulum membranaceum situated 

 beside it. The fenestra of the vestibulum membranaceum is to 

 be compared to the fenestra ovalis in man, and the fenestra of 

 the vestibulum cartilagineum to the fenestra rotunda in man. 

 The fenestra of the vestibulum cartilagineum forms an opening 

 into the cavity of the vestibulum cartilagineum, the fenestra of 

 the vestibulum membranaceum in like manner forms an opening 

 into the cavity of the vestibulum membranaceum. 



20. Between the fenestras of the vestibula membranacea cut 

 out in the cartilaginous cranium (belonging to the right and left 

 ear) and the skin covering the occiput, two bags are interposed 

 iilled with a white calcareous liquor, and touching each othei*. 

 From each of these, a large membranous canal entering through 

 the fenestra of the vestibulum membranaceum, descends into 

 the vestibulum membranaceum, and tills its cavity. These bags 

 called by Weber the sinuses of the external ear, and compared 

 by Monro to the conchee of the human ear, answer the purpose 

 of the cavity of the tympanum, and the liquor included in them 

 serve the purpose of the bones of the ear. 



21. One or more very small canals, detected by Monro ; but 

 not found by Camper, Scarpa, Comperetti, and Cuvier, pass from 

 the auditory sinus of each side to tlie cutis, and there open by 

 very small mouths. By these canals, any excess of the calca- 

 reous liquid contained in the sinus auditorius may be thrown 

 out. 



22. There is a small muscle belonging to each auditory sinus, 

 by means of which the auditory sinus may be compressed, and 

 its liquor either thrown out through the small apertures opening, 

 in the cutis, or impelled through the canal into the membranous- 

 vestibulum. In this way the vestibulum membranaceum maybe 

 either compressed or relaxed. 



23. The vestibulum membranaceum of the raia sarpedo mar- 

 morata (Risso) does not contain white cretaceous lapilli ; but a 

 gelatinous mass, mixed with a black coloured sandy matter. 



24. The membranous semicircular canals of the raiae are joined 

 to each other and to the vestibulum membranaceum in quite a 

 different manner from those of the squalus carcharias (white 

 shark). The semicircular canals of the squalus carcharias have 

 a semicircular form, while that of the raia has a circular form. 

 The semicircular canals of the squalus carcharias proceed by one 

 extremity from the vestibulum membranaceum, and by the other 

 extremity return into it ; whereas those of the raise are quitb 



