1894.] NATURAL SCIENCES OF PHILADELPHIA. 35 



nem proteusam crassiusculara & inaequalem lineam, annulo sen 

 circulo, autea nomiuato, subjectara &c. paulo lougius pvotensam. 

 Os itaque teinporum hoc meuse tribus constat ossiculis, annulo 

 scilicet,'^ osse squamoso et illo jam comraemorato. 



Further, according to Kerckringius the "pyriforma" (prootic) 

 coalesces at the sixth month with the "scutum ovale" (epiotic) to 

 form one bone, the latter being joined at the seventh month by the 

 " tertium illud ossiculum" (opisthotic), whereas, as we shall show, 

 it is the opisthotic and not the epiotic that combines with the prootic 

 to form the pars petrosa. As to what Kerckringius meant by his 

 " tria petrosi ossis distincta ossicula," we will try to make clear in 

 our description of the manner in which the petromastoid develops 

 in Man. 



The work ' ' De Aure Humana " by Cassebohm appeared in 1734- 

 1735. The description of the development of the ear given by 

 this author, while agreeing in the main with that of Kerckringius, 

 differs from it in some respects. Cassebohm recognized, however, 

 with Kerckringius, the fact of the pars petrosa being more or less os- 

 sified before the appearance of the "tria ossicula," as shown by 

 numerous passages in his text as well as by his excellent figures.' 



In the judgment of the author, Meckel, rather than Kerckringius 

 or Cassebohm, was the first anatomist to describe the petromastoid of 

 the temporal bone as arising from three distinct centres of ossifica- 

 tion. According to this author* the first part of the labyrinth to os- 

 sify is that immediately surrounding the fenestra rotunda, whence 



-' Kerckringius, loc. cit. 



^Tractatus Quatuor Anatomici de Aure Humana. Halae Magdeburgicae, 

 1734 p. 19:--"Kerckringii relatio de osse temporuni in foetu trium meusium, 

 cum mea observatione de tbetu totidem couvenit excepto. . . . Idem ille 

 porro in foetu quinque mensium, partem petrosam, circa processum mastoideuni 

 tria ossicula habere refert, quorum due mense sexto coaulere : verum in his 

 mensibus. in loco indicate nulla ossa peculiariased cartilaginem vidi Tab. 3. Fig. 

 22, lit. K." 



Tractatus tiuatuor &c., p. 45: — Antetiuam tympani membranam removebam, 

 cochleae tnl)er membranae hujus partem superiorem & niediam tangebat & 

 tiuani vis cartilaginem esset, foraminis tanien rotundi (quod ad cochleam & 

 ducit & pertiuet) margo erat osseus partem que annuli posteriorem attingebat." 

 . . . . Cochleae que tuber ex fusco (juem habebat, colorem nigrum acquisi- 

 visset, tunc foraminis rotundi margo allius osseus que apparebat." 



Tractatus Quintus Anatomicus. Halae Magdeburgicae, 1735, p. 15 : — " In foetu 

 trium mensium cochleam, circa foramen rotundum osseam, reliquam vero coch- 

 leae partem cartilagineam. In foetu quatuor mensium cochleam vidi osseam, 

 excepta lamina spirali, quae cartilaginea erat ; banc in foetu quinque mensium 

 osseam demum conspexi." 



* Handbuch der Menschlichen Anatomic, Band 4. Halle & Berlin, 1820, p. 49. 



