290 ROBERT J. TERRY 



foramen. Outside the wall a corresponding groove separates 

 the paracondyloid process (figs. 2, 3) from the pars canalicularis 

 of the otic capsule. The caudal free margin of the lateral occipi- 

 tal arch enters into the boundaries of the foramen magnum 

 (figs. 1, 2, 3). Its ventral portion forms the larger part of 

 the occipital condyle; its dorsal portion, a rough angular process 

 directed medially. The processes of opposite sides mark the 

 dorsal limit of the foramen magnum at this stage and afford at- 

 tachment to the spino-occipital membrane. Dorsad of the 

 level of these processes the lateral occipital arches are continued 

 into the broad, curved posterior portions of the parietal plates, 

 between which the tectum posterius extends in an arch from 

 side to side. 



Within the cranium, at the junction of basal plate and lateral 

 occipital arch, is a rounded prominence, the cartilaginous pre- 

 cursor of the tuberculum jugulare, separating the entrance 

 to the hypoglossal canal from the fossa occipito-canalicularis 

 (fig. 1). At its cephalic end, this elevation, broadening con- 

 siderably, becomes continuous with the basi-vestibular commis- 

 sure (figs. 9, 10, 19). This commissure is united with the otic 

 capsule at the boundary between the medial wall of the promi- 

 nentia utriculo-ampullaris inferior and the cochlear capsule, 

 and forms here a prominence making the posterior wall of the 

 internal acustic meatus. The jugular tubercle, which presents 

 much more the form of a ridge than of a tubercle, stands within 

 the cranium opposite the paracondyloid process. Both pro- 

 cesses contribute to the formation of the deep caudal wall of the 

 jugular foramen, a relation observed by von Noorden in the 

 human embryo. The occipito-canalicular fossa lies between the 

 inferior ampullary eminence and the basivestibular commissure 

 and connects the sigmoid sulcus with the jugular foramen. 



The jugular foramen (figs. 1, 2, 12) when viewed from within 

 the cranium is crescentic, the convex side being formed caudally 

 by the tuberculum jugulare and medially by the commissura 

 basivestibularis ; the concave margin, directed laterad, is consti- 

 tuted by the medial wall of the prominentia utriculo-ampullaris 

 inferior. The vena jugularis interna and the accessorius, vagus 



