The Chondrocrunium of an Embryo Pig. 187 



backward are the long cornua hranchialia I, the homologs of the cor- 

 nua majora in human anatomy. 



The cartilaginous forerunners of the ear-bones, as said above, 

 lie outside the general surface of the primordial cranium, the maUeus 

 and inctis outside and the stapes within, its plate lying in the fenestra 

 vestibuli. This opening into the inner ear, the fenestra ovalis of 

 human anatomists, is here large and triangular, with one side hori- 

 zontal and the opposite angle directed ventralward. It is only 

 about one-third filled by the stapedial plate (Fig. 4, st). Later the 

 plate fits snugly, due, in part, to the growth of the stapes, and in 

 part to the constriction in the size of the fenestra. In the adult 

 the opening is so small that the plate of the stapes will not pass 

 through it. The stapes is a thick oval ring of cartilage, with the long 

 axis lying in an antero-posterior direction. Its median side is some- 

 what the heavier and is flattened to form the stapedial plate. Be- 

 tween the plate and the edge of the fenestra vestibuli is a layer of 

 denser connective tissue, the Aiilage of the ligamentum annulare 

 stapedis (Fig. 4). There is no stapedial artery, although its earlier 

 presence is indicated by the shape and arrangement of the cells 

 within the stapedial foramen. The musculus stapedius (Fig. 3, 

 m. st.) is inserted on the postero-lateral part of the stapedial ring; 

 from thence it runs backward in the narrow sulcus facialis. 



Immediately in front of the insertion of the musculus stapedius 

 the stapes articulates with the crus longum incudis by a dense layer 

 of tissue, the Anlage of the processus lenticularis. This is plainly 

 a part of the incus, a further proof that the os lenticularis of the 

 earlier anatomists in not a distinct bone. From its attachment with 

 the stapes, the crus longus curves outward and upward to the corpus 

 incudis. This is short and thick and extends forward a short dis- 

 tance to where it ends in a saddle-shaped articular surface, the two 

 forwardly-projecting points of which are medianly and laterally 

 placed. The crus breve incudis extends posteriorly from the corpus 

 to the crista parotica, to which it is attached by the ligamentum 

 incudis posterius. 



The malleus articulates with the above-mentioned articular surface 

 of the incus and is continued forward, without interruption, into 



