326 



STUDY OF PIG EMBRYOS. 



two irregular cavities, the nasal chambers. The two cavities are separated from 

 one another by a broad mass of tissue, the nasal septum, the ventral edge of which 

 at this stage forms a portion of the roof of the mouth-cavity. In the center of the 

 nasal septum is a broad band, Sept, of denser mesenchymal tissue, the anlage of 

 the cartilaginous septum of the nose. On either side of the nasal septum is the 

 irregularly shaped nasal cavity, which opens into the mouth between the ven- 

 tral edge of the nasal septum and the inner edge of the maxillary process. The 



arach. ' Sk. 



Mdb. 



FIG. 220. PIG, 20.0 MM. FRONTAL SECTION OF HEAD. SERIES 40, SECTION 84. 



arach, Arachnoid membrane. H, Cerebral hemispheres. Max.tb, Maxillo-turbinal fold. Mdb, Mandible. MX. 

 sup, Superior maxillary nerve. Nas.tb, Naso-turbinal fold. N.olf, Olfactory nerve. Sept, Cartilaginous 

 septum of the nose. Sk, Mesenchymal anlage of the dura mater and skull. Ton, Tongue. X 18 diams. 



medial side of each nasal cavity is comparatively regular, but- the external side 

 shows two prominences, each of which is formed by a mass of mesenchymal tissue 

 covered by epithelium. The upper of these projections, nas.tb, is the anlage of 

 the naso-turbinal fold, and the lower, max.tb, the anlage of the maxillo-turbinal 

 fold. In the nasal septum itself are two oval rings of epithelium, sections of 

 Jakobson's organs. This organ is an evagination of the epithelial lining of the 

 nasal cavity, which opens anteriorly and extends backward some distance in the 

 nasal septum. In the maxillary process may be observed the superior maxillary 

 nerve, Mx.sup. The number of cells in the nerve has increased, and consequently 



