MINUTE STRUCTURE OF MEMBRANOUS LABYRINTH. 759 



superior and external semicircular canals enter the cavity in a group along 

 the crista vestibuli ; the fibrils for the sacculus enter the vestibule by a 

 smaller group of foramina, which are situated below those just described, 

 and open at the bottom of the fovea hemispherica ; the branch for the pos- 

 terior semicircular canal is long and slender, and traverses a small passage 



Fig. 515. 



Fig. 514. 



r 



'" 



Fig. 514. TRANSVERSE SECTION OF ONE OP THE MEMBRANOUS SEMICIRCULAR CANALS 

 (from Kolliker). ^ 



This specimen is from the ear of the calf : a, external fibrous layer with interspersed 

 nuclei ; 6, homogeneous layer ; c, epithelial lining. 



Fig. 515. AMPULLA OF THE SUPERIOR AND EXTERNAL SEMICIRCULAR CANALS AND PART 

 OF THE COMMON SINUS SHOWING THE ARRANGEMENT OF THE NERVES (from Steifen- 

 sand) . %- 



1, membranous ampulla of the superior canal ; 2, that of the external canal ; 3, part 

 of the common sinus ; 4 and 5, fork-like swellings of the nerves at their ampullar dis- 

 tribution ; 6, twig of the auditory nerve spreading in the common sinus. 



in the bone behind the foramina for the nerve of the sacculus. The nerves 

 of the ampullae enter the flattened or least prominent side of the ampullaa, 

 where they each form a forked swelling, which corresponds with the trans- 

 verse septum already described, in the interior of the dilatation. No 

 filaments have been fuund extending to any other parts of the semicircular 

 canals. 



Microscopic structure. The walls of the common sinus, sacculus and 

 membranous semicircular canals are in general semitransparent ; but they 

 are thicker and more opaque where nerves and vessels enter. On the 

 outer surface is a layer of minutely ramified blood-vessels and loose tissue, 

 which contains irregular pigment- cells : within this is a transparent layer, 

 faiutly fibrillated, and presenting elongated nuclei when acetic acid is added ; 

 lining the interior is an epithelial layer of polygonal nucleated cells. 

 The mode of ending of the nerves in the membranous substance of the 

 vestibule and semicircular canals is difficult to investigate, on account of 

 the minuteness and delicacy of the parts ; for this reason also observers 

 have had recourse in great measure to the examination of the vestibule 



