180 Charles Searing Mead. 



is there a special foramen for the carotid artery, which here enters 

 the cavuni cranii throngli the large slit between the processus clino- 

 idens posterior and the processus alaris. 



AuDiTOKY Capsules. 



The position of the auditory capsules has already been described. 

 Their demarcation from the rest of the cranium is sharp and dis- 

 tinct. The general shape of each capsule is that of an ovoid body, 

 the long axis of which is obliquely placed in relation to the long 

 axis of the skull. The smaller end is located anteriorly and is 

 directed downward and inward; the larger end is situated poste- 

 riorly and points upward and outward. 



The auditory capsules are divided into two parts, the 'pars 

 cochlearis, containing the sacculus and the cochlea, and the pars 

 vestibularis, in which the utriculus and semi-circular canals are 

 located. The nearly spherical pars oochlearis (PI. II) occupies 

 the antero-median two-fifths, while the larger pars vestibularis (PL 

 III), resembling a three-sided pyramid in shape, completes the 

 postero-lateral three-fifths. The median faces of the two parts form 

 together a surface, which is concave in a transverse direction and 

 which conforms to the general internal surface of the cavum cranii. 



The pars vestibularis presents an outer surface which is that of 

 an equilateral triangle, one side of which is next to the pars cochlearis 

 and the mandibular and hyoid arches, one next to the lamina parie- 

 talis (foramen jugulare spurium), while the third borders on the 

 lateral parts of the regio occipitalis. This surface is arched in an 

 antero-posterior direction, the convexity being outward. Its edges 

 are formed by the ridges of the semi-circular canals {prominentim 

 setni-circularce) , those of the posterior and lateral canals being the 

 most prominent. That of the lateral canal takes part in the formation 

 of the crista parotica and the processus perioticus superior (PL III). 

 In the central area between the ridges are a number of small pits 

 (8-10), some of which penetrate the wall and open into the fossa 

 subarcuata. They persist throughout life and serve for the passage 

 of small veins w^hieh carry blood to the sinus transversus. The 

 ampullae form no distinct swellings on the outside of the capsules, 

 such as Fischer described in Talpa. 



