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chus. — In Scaphirhynchus the olfactory /odes are ovoid tuber- 

 osities upon the cephalo-lateral aspects of the hemispheres, 

 with their longer diameter in the axes of the strongly divari- 

 cated olfactory nerves (Plate XI, Fig. 15). Cephalad, they 

 are completely closed, and a considerable ventricle occupies 

 the centre (Fig. i, Plate XI). Caudad, where they pass into 

 the cerebrum, they stand in communication with the hemi- 

 spheres, and are roofed over only by the thin pallium or 

 dorsal lamina of the cerebrum. 



The histological structure is similar to that in reptiles, 

 save that the specific cells are relatively more elongate and 

 more sparingly distributed, nowhere forming a connected 

 layer. The glomerulary layer is highly developed, and there 

 is a noticeable absence of the Deiter corpuscles, so usual an 

 accompaniment of the glomerules. The neuroglia layer, 

 between the glomerules and the inner granular zone, is wide, 

 and contains few very irregular elongated cells with large, 

 pale, round nuclei. 



These cells are of the most various forms, often having a 

 long, apical process, and two or more basal processes, but 

 the relations may be reversed. Frequently these cells are 

 seen between the massed glomerules, occupying the irregular 

 interspaces. There are also cells of irregular shapes and 

 more deeply stained, which are scattered among the above. 

 These are, perhaps, to be compared with the rhinomorphic 

 cells elsewhere referred to. The granular zone is well 

 developed. The epithelium is many-layed. 



In sections of Scaphirhynchus caudad to the point where 

 the olfactory opens into the lateral ventricle (Plate XI, Fig. 

 3), there is a rapid eversion of the hemisphere, causing the 

 olfactory portion to be carried ventrad and laterad. A small 

 groove separates a projection which is adjacent to the 

 olfactory from the basal portion of the hemisphere (see right 

 side of the figure quoted). This may be called the ala,and it 

 contains concentrically arranged cells. The segment of the 

 cerebrum remains distinct in structure from the basal portion. 



