310 ROBERT J. TERRY 



and blood vessels (indicated by ** fig. 2) . The latter find a pas- 

 sage to the cranial cavity by the opening in the fossa behind the 

 eminentia cruris communis (vide supra); veins passing out of 

 this opening join the sigmoid sinus. The space extends cephalo- 

 caudad and dorsad, approaching the anterior and posterior 

 semicircular canals and the crus commune, and reaching ventrad 

 as far as the level of the roof of the vestibular cavities and the 

 crista inter vestibular is. It does not at any point communicate 

 with the vestibule. 



Lamina parietalis (figs. 1, 2, 3, 4). This plate of cartilage stands 

 in a sagittal plane dorsad of the pars canahcularis. The concave 

 extracranial surface gives origin to part of the temporal muscle; 

 the convex intracranial surface is smooth. The parietal plate is 

 broad anteriorly and posteriorly and narrow between where it 

 lies dorsad of the pars canalicularis of the otic capsule. It goes 

 over anteriorly into the commissura orbito-parietahs posteriorly 

 into the lateral occipital wall, and, in connection with these two 

 parts, is fixed to the pars canalicularis. Between the four ele- 

 ments named is the foramen jugulare spurium, narrow and 

 curved around the dorsal circumference of the otic capsule. 

 Some minute veins traversing the foramen connect the transverse 

 sinus with extracranial veins. The foramen of the right side is 

 subdivided by a cartilaginous connection of the parietal plate 

 and pars canalicularis. The hinder of the two resulting foramina 

 is located opposite the summit of the posterior semicircular 

 canal. In van Wijhe preparations of embryos 24 to 30 mm. in 

 length, union of the parietal plate and pars canalicularis was ob- 

 served dividing the spurius jugular foramen into two parts. 

 This connection was found on one side or the other, rarely on 

 both, occurring, as in the stage modeled, at the summit of the 

 anterior semicircular canal. The parietal plate at this level is 

 very narrow, is notched in its dorsal margin and, compared with 

 the regions anterior and posterior, is less chondrified. 



