THE SKIN AND SENSE ORGANS 297 



The older authors (Hasse, Kuhn, and Retzius) imagined that this 

 space contained perilymph, and that the labyrinth simply floated free 

 in this fluid supported by a few strands of connective tissue. Harri- 

 son (1902) showed that this was not the case and that the perilymph 

 was restricted to certain definite regions (see below), while the re- 

 maining space between the labyrinth and the capsule was occupied 

 by a tissue which he termed perilymphatic tissue. This is a connective 

 tissue which becomes specially dense, 'almost cartilaginous', around 

 the labyrinth itself. 



The following may be termed the 'intrinsic' portions of the ear — 

 thrtt semicircular canals with their ampullae^ the utriculus^ the sacculus^ 

 the lagena^ pars basilaris and pars neglecta^ and the ductus endolym- 

 phaticus. The 'extrinsic' portions are the perilymph system and the 

 saccus endolymphaticus. 



The semicircular canals are not all equal in extent or in curvature. 

 The shortest, and at the same time the most nearly circular, is the 

 posterior canal (can.s.p.). It lies in a vertical plane pointing in a 

 postero-lateral direction relative to the axis of the body. It may be 

 supposed to arise from the pars superior utriculi just behind the an- 

 terior canal, and, after completing almost an entire circle, it re-enters 

 the utriculus at t\\^ pars posterior ]\x^\. below the origin of the horizontal 

 canal. Its ampulla is situated at the ventral end (amp. p.). 



The horizontal canal (can.s.h.) (or canalis externus, Kuhn) arises 

 from the pars posterior utriculi between the two ends of the posterior 

 canal. The curvature is not quite even throughout its length. The 

 posterior portion describes roughly the quadrant of a circle and is 

 then succeeded by a more flattened mesial portion. Finally the 

 anterior end bends round more sharply again and enters the recessus 

 utriculi close to the anterior canal. It does not lie in a truly hori- 

 zontal plane relative to the other canals, but is slightly depressed 

 anteriorly. The ampulla is at the anterior end (amp.h.). 



The anterior canal (can.s.a.) arises from the sinus superior utriculi 

 close to the posterior canal, and lies in a vertical plane pointing in an 

 antero-lateral direction. It remains almost flat for about two-thirds 

 of its length and then bends sharply ventralwards to enter the dorsal 

 aspect of the recessus utriculi. The ampulla is at the anterior end 

 (amp. a.). 



The utriculus is a wide tube, more or less saddle-shaped, sitting 

 over the mesial part of the sacculus. Its most dorsal portion, the 

 broad sinus superior (s.s.utric), gives rise to the anterior and posterior 

 canals, while its anterior end dips ventralwards to the recessus utriculi 

 (rec.utric), which is the expanded portion into which the ampullae 



