326 ROBERT J. TERRY 



of the hypophyseal cartilage. The trabecular plate makes its 

 appearance in embryos of the present stage (fig. 17), consisting 

 of a single thick mass of young cartilage continuous anteriorly 

 with the beginnings of the septum nasi. Caudally it reaches 

 almost to the hypophyseal cartilage. In the van Wijhe prepara- 

 tions the limits of the trabecular plate are clearer than in the sec- 

 tions (fig. 6). On its dorsal surface the sulcus chiasmaticus 

 appears; on its sides, the beginnings of the pre- and metoptic 

 processes. 



In a frontal section passing through the hypophysis and coch- 

 lear canal of an embryo of 12 mm. (fig. 16) the carotid artery ap- 

 pears in its course through the cranial wall. It lies in an oval 

 area of less dense mesenchyma than that a little wa> behind its 

 position. The denser tissue anterior to the area forms a curved 

 bar, continuous with the side of the hypophyseal cartilage medi- 

 ally, thence extending in a curve outside the artery toward the 

 cochlear capsule. This will be referred to as the commissural 

 element; it is the beginning of the processus alaris and commis- 

 sura alicochlearis. The oval, hght area about the carotid is lim- 

 ited caudally and medially by the cochlear capsule and a bridge 

 of mesenchyma (future basicochlear commissure) stretching from 

 the latter to the hypophyseal cartilage. 



In the mesenchyma laterad of the commissural element is a 

 small condensation beneath the Gasserian ganglion, which proves 

 to be part of the medial extremity of the future ala temporalis. 

 This condensation will be refered to as the alar element. The 

 less dense mesenchyma between the latter and the commissural 

 element extends obliquely from before, backward and outward. 

 The mesenchyma of the alar element becomes broader and denser 

 as it extends laterally; its caudal concave margin, pressed against 

 the mandibular nerve, forms the primitive incisura ovalis ; within 

 its anterior part appears the maxillary nerve. The ophthalmic 

 nerve (whose ganglionic cells are in part separate from the semi- 

 lunar ganglion) passes over the alar element toward the eye. 

 The van Wijhe specimens of 12 mm. (fig. 6) show a small darkly 

 stained nodule far removed from the hypophyseal cartilages and 

 lying immediately ventrad of the anterior end of the semilunar 



