THE INTERNAL EAR. 1515 



backward and downward to the opening of the posterior ampulla, a distance of from 

 5. 5-6 mm. The utricle is made up of three subdivisions, the uppermost of which is 

 respresented by a blind sac, from 3-3.5 mm. in length and breadth, called the 

 recessus utriculi, whilst the two lower divisions together form the utriculus pro- 

 prius, which measures 3 mm. by from 1.5-2 mm. The lower part of the utricle 

 proper is prolonged into the tube-shaped sinus posterior, which connects the am- 

 pulla of the posterior semicircular canal with the utricle. 



The openings of the semicircular canals into the utricle are disposed as 

 follows : into the recessus utriculi open ( i ) the ampulla of the superior semicircular 

 canal and (2) that of the horizontal canal. Into the ritriculus proprius open (3) 

 the sinus superior, which lies within the crus commune and receives in turn the 

 nonampullated ends of the superior and posterior semicircular canals; (4) the non- 

 ampullated end of the horizontal semicircular canal ; and (5) the ampulla of the 

 posterior semicircular canal through the sinus posterior. On the antero-lateral wall 

 of the recessus utriculi is placed the macula acustica of the utricle, whilst from its 



FIG. 1269. 



Hamulus Helicotrema 



Facial canal 

 Vestibular( oval) window 



Pyramid 



Tympanic cavity/' / - 



/ 

 Promontory 



Probe passes through cochlear (round) window Lamina spiralis secutidaria 



Right bony cochlea partially exposed by section passing through outer wall of apex and of first turn. 



antero-mesial wall springs the canalis utriculo-saccularis, the small canal from the 

 utricle that joins even a smaller passage from the saccule to form the ductus 

 endolymphaticus. 



The Saccule. The saccule (sacculus) is an irregularly oval compartment, about 

 3 by 2 mm. in size, which occupies the recessus sphaericus in the lower and anterior 

 part of the vestibule, to which it is attached by connective tissue. It is somewhat 

 flattened laterally and at its lower end gradually narrows into a passage, the canalis 

 reuniens, which connects the saccule with the ductus cochlearis. Its upper end 

 bulges backward forming the sinus utricularis, whose wall comes in contact with 

 that of the utricle. The small canal, already mentioned as helping to form 

 the ductus endolymphaticus, arises from the posterior wall of the saccule. The 

 ductus endolymphaticus passes through the aquaeductus vestibuli to end in a 

 blind dilated extremity, the saccus endolymphaticus, lying between the layers 

 of the dura mater below the opening of the aqueduct. Through the openings in 

 the recessus sphaericus branches of the vestibular nerve enter and pass to the 

 macula acustica sacculi on the anterior wall of the saccule. The canalis reuniens 

 is the very small tube passing from the lower part of the saccule into the upper 

 wall of the cochlear duct near the caecum vestibulare, as its blind vestibular end 

 is called. 



The Membranous Semicircular Canals. These tubes (ductus semicircu- 

 lares) occupy about one third of the diameter of the osseous canals and correspond 



