358 CHARLES CLIFFORD MACKLIN 



recess. In its ventral area may be seen the inferior utriculo- 

 ampullary prominence, continuous dorso-laterally with the 

 posterior semicircular prominence and ventrally with the short 

 interperilymphatic process. A spur of the inferior utriculo- 

 ampullary prominence caused by a localized thickening of the 

 wall, projects backwards and upwards as a low ridge to disappear 

 somewhat below the endolymphatic foramen. It overhangs 

 the transverse sinus in this region. The fossa subarcuata pos- 

 terior, which Voit mentions in his description of the skull of the 

 rabbit, is not represented here. 



The boundaries of the ventral surface (fig. 6) have already been 

 described in connection with the discussion of the ventral bound- 

 aries of the lateral and medial surfaces. Its medial part is con- 

 cerned with the junction of the pars canalicularis with the vestib- 

 ular portion of the pars cochlearis. The lateral part of the 

 ventral surface forms the dorsal wall of the ventro-lateral otic 

 recess, which has been already referred to, and which contains 

 the structures entering into the formation of the middle ear. 



In the cranial area of the ventral surface there appears, pro- 

 jecting forward from the ventral surface of the superior utrio- 

 uloampullary prominence, a distinct, almost vertical, ridge 

 (figs. 5 and 6), which lies immediately medial to the body of the 

 malleus, but is separated therefrom by a sheet of connective 

 tissue. This represents the medial part of the cartilaginous 

 tegmen tympani, or processus perioticus superior. The lateral 

 portion of the tegmen, such as is shown in Voit's model of the 

 skull of lepus, is not present, but its position is indicated by a 

 low ridge, which arches downward and outward from the upper 

 end of the medial portion of the tegmen and marks off the ven- 

 tral from the lateral surface, terminating below in the crista 

 parotica (fig. 6). The cartilage is not developing rapidly in this 

 location, as in Voit's specimen. Upon examining the model of 

 Hertwig it is found that the tegmen tympani has grown forward 

 and outward to overlie partially the bodies of the malleus and 

 incus, but the lateral portion has evidently made no further 

 development, and so it may be concluded that the ossicles in 

 man do not occupy a deep cartilaginous recess formed by the teg- 



