THE EAR, HEARING, TASTE AND SMELL 191 



in the bony one, consists of two sacs communicating by a narrow 

 aperture. The posterior is called the utriculus, and into it the 

 membranous semicircular canals open. The anterior, called the 

 sacculus, communicates by a 

 tube with the membranous coch- 

 lea. The membranous semicir- 

 cular canals much resemble the 

 bony, and each has an ampulla; 

 in most of their extent they are 

 only united by a few irregular 

 connective-tissue bands with the 

 periostcMn lining the bony ca- 

 nals ; but in the ampulla one side 



Of the membranous tube is FIG. 72.-A section through the cochlea 



closely adherent to its bony pro- in the line of its axis - 

 tector; at this point nerves enter the former. The relations 

 of the membranous to the bony cochlea are more complicated. 

 A section through this part of the auditory apparatus (Fig. 72) 

 shows that its osseous portion consists of a tube wound two and 

 a half times (from left to right in the right ear and vice versa) 

 around a central bony axis, the modiolus. From the axis 

 a shelf, the lamina spiralis, projects and partially subdivides 

 the tube, extending farthest across in its lower coils. At- 

 tached to the outer edge of this bony plate is the membranous 

 cochlea (scala media), a tube triangular in cross-section and at- 

 tached by its base to the outer side of the bony cochlear spiral. 

 The spiral lamina and the membranous cochlea thus subdivide the 

 cavity of the bony tube (Fig. 73) into an upper portion, the scala 

 vestibuli, SV, and a lower, the scala tympani, ST. Between these 

 lie the lamina spiralis (ho) and the membranous cochlea (CC), the 

 latter being bounded above by the membrane of Reissner (R) and 

 below by the basilar membrane (6). The free edge of the lamina 

 spiralis is thickened and covered with connective tissue which is 

 hollowed out so as to form a spiral groove (the sulcus spiralis, ss) 

 along the whole length of the membranous cochlea. The latter 

 does not extend to the tip of the bony cochlea; above its apex the 

 scala vestibuli and scala tympani join; both are rilled with peri- 

 lymph, and the former communicates below with the perilymph 

 cavity of the vestibule, while the scala tympani abuts below on the 



