The Chondrocranium of an Embryo Pig. 183 



flicting evidence at hand, i. e., the shape and depth of the fossa, I 

 do not think we are in a position to say which is the primary and 

 which the secondary condition. Before this question can be deter- 

 mined, it will be necessary to study more closely the relations of 

 the surrounding elements. 



Externally on the antero-ventral face of the pars vestibularis 

 is a deep groove, the sulcus facialis, the anterior two-thirds of which 

 is occupied by the nervus facialis, while the stapedial muscle is 

 located in its posterior half, the two running side by side for a 

 short distance, with the muscle on the median side (Fig. 3). The 

 latter, in cross-section, is about one-sixth the size of the nerve. The 

 position and shape of the groove is similar to that in Lepus, Sem- 

 nopithecus and human chondrocrania, but differs from that in Talpa, 

 where its posterior portion is enlarged to form an oval pit which is 

 placed more on the outer side of the lateral semi-circular canal. Its 

 large size in Talpa is due not only to the large size of the stapedial 

 muscle but also to the digastric muscle, which has its origin in this 

 cavity. In Sus this latter muscle arises on the processus paroccipi- 

 talis. The lateral wall of this groove is formed by the crista parotica 

 (PI. Ill and Fig. 3, or. par.), which is located on the antero-ventral 

 face of the prominentia semi-circularis lateralis. At the middle of 

 its length is attached, by connective tissue, the hyoid arch (Reichert's 

 cartilage). To the middle of the crista the processus brevis of the 

 incus is attached by a ligament. At the anterior end of the crista 

 is a prominence which later develops into the processus perioticus 

 superior {legmen tympani) (PI. III). There has been considerable 

 confusion over the homologies of the processus perioticus superior 

 and the crista parotica. Gaupp (1900) described and figured a 

 process in a Lacerta embryo, which he called the crista parotica. 

 This he homologized with the processus perioticus superior (tegmen 

 tympani) of mammals, and Fischer (1901 b) supported him. It 

 remained for van Kampen (1905, p. 345) to show that the processus 

 perioticus superior is a new structure in the mammals, and that the 

 processus facialis is the homolog of the reptilian crista parotica. 



Antero-ventrally and somewhat internal to the pars vestibularis 

 lies the balloon-shaped pars cochlearis (PI. II and Fig. 4, coch.). 



