Fig. 5. Otic capsule developmental stages 160 mm and 170 mm fetus
Drawings, continued, of the stapes and the adjacent ﬁssular region of the otic capsule, depicting developmental stages; X 6.6. Parts a to c are from a 160 mm. (19.5 week) fetus (Wisconsin series 41: (a) slide 19, section 4; (b) slide 18, section 8; (c) slide 17, section 9). d to f, from a 170 mm. (20 week) fetus (Wisconsin series 131: (d) slide 25, section 5; (e) slide 21, section 10; (f) slide 20, section 8). Here, a is taken at the level of the tympanic oriﬁce of the ﬁssula ante fenestram; 19, through the middle of the ﬁssular tract and the posterior crus of the stapes; c, through the vestibular oriﬁce of the ﬁssula, and d to- f, from sections of the 170 mm. fetus which pass through similar levels of the ﬁssula and ossicle (in succession, the tympanic extremity, the body and the vestibular extremity of the fisstula).
In the 160 mm specimen destruction of cartilage is under way; bone is formed on the obturator aspect of the base and crus of the stapes and on the tympanic and vestibular walls of the otic capsule. Concurrently, the cartilage of the ﬁssula has become partially separated; while almost detached at its cochlear end, the ﬁssular cartilage is still broadly continuous with similar tissue at the vestibular window.
In the 170 mm fetus newly formed bone is present on both aspects of the crus as a complete shell externally, as a foraminous wall internally (i. e., toward the obturator foramen).
Anson BJ. and Cauldwell EW. Stapes, fissula ante fenestram and associated structures in man: V . From the fetus of 160 mm to term. (1948) 48(3): 263-300.
Cite this page: Hill, M.A. (2019, June 15) Embryology Anson1948 fig05.jpg. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/File:Anson1948_fig05.jpg
- © Dr Mark Hill 2019, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G
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