SKULL OF A HUMAN FETUS OF 40 MM. 355 



by the out-bulging of the anterior semicircular canal; it is known 

 as the prominentia semicircularis_ anterior. Ventrally this prom- 

 inence terminates in the prominentia utriculo-ampullaris supe- 

 rior, a conspicuous rounded eminence at the cranio-ventral extrem- 

 ity of the pars canalicularis, marking the upper approximation 

 point of its three surfaces. It is formed principally by the wall 

 of the ampulla of the anterior semicircular canal (fig. 8). Spring- 

 ing upward from the dorsal part of the anterior semicircular 

 prominence the capsuloparietal commissure may be seen, its 

 connection with the otic capsule being shown in figures 6 and 7. 

 Dorsal to this the border is marked by the capsuloparietal fissure 

 (fig. 3), and caudal to this again by the lower union of the parietal 

 plate with the otic capsule; under the latter union is to be noted 

 the capsulooccipital fissure (fig. 7). The lowermost part of this 

 border is formed by union with the squama. These borders 

 separate the lateral from the medial surface of the capsule. 



Both the capsuloparietal and capsulooccipital fissures appear 

 in other models of the human skull (Levi, Hertwig), and they 

 have also been shown to be present in the primitive skulls of 

 other mammals, as the ape (Fischer) and rabbit (Voit). The 

 capsuloparietal fissure is sometimes known as the foramen jugu- 

 lare spurium, and the capsulooccipital fissure as the foramen 

 petrosooccipitale. 



The ventral border, which separates the lateral from the 

 ventral surface, is, below the superior utriculoampullary prom- 

 inence, marked off mainly by the conspicuous crista parotica, 

 below this by the mastoid process, and below this again by the 

 prominentia semicircularis posterior (fig. 6), which passes over 

 the root of the mastoid process at this point. 



The most prominent object upon the lateral surface is the 

 lateral otic eminence (fig. 6), which lies in its dorso-cranial area, 

 separated from the dorsal part of the anterior semicircular 

 prominence by a very shallow groove. It slopes backward into 

 the parietal plate between the two post-otic fissures, and is formed 

 by the backward and outward projection of the massa angu- 

 laris, a large mass of cartilage lying in the enclosure formed 

 by the anterior and lateral semicircular canals, the crus com- 



THE AMERICAN JOURNAL OF ANATOMY, VOL. 16, NO. 3 



