1891.] MICROSCOPICAL JOUENAL. 51 



obliterated canal is-an axis which is composed of granules, broken-down 

 endymal cells, and capillaries. 



Of the species of wild canidaj examined, the brain of the coyote had 

 been poorly preserved in alcohol, and the olfactory bulb had become 

 somewhat distorted, rendering it undesirable for the study of its struc- 

 tural elements. A small central cavity, however, was easih' seen ; but 

 the end3'mal cells, on account of maceration, had probably become dis- 

 integrated and finally disappeared. In the crus the cavity had become 

 entirely closed up. The dingo's brain, also preserved in alcohol, was 

 in a much better condition. The cavity of the olfactory bulb was very 

 distinct and relatively large ; at certain points a few endymal cells still 

 adhered to its border. The cavity of the crus, however, as in the other 

 specimens, was completely occluded. 



In the larger domestic dogs, especially the Shepherd and Newfound- 

 land, the gross appearance of the olfactory lobes resembles very much 

 that of the wild species, on account of the projection of the bulbs 

 beyond the cerebrum. In the terrier and spaniel the increased develop- 

 ment of the frontal lobes causes the cerebrum to overlap the bulbs. 



A study of embryonic conditions may demonstrate when the process 

 of occlusion begins, and would be a most important auxiliary to our 

 complete understanding of existing facts. 



CONCLUSIONS. 



1. That facts do not warrant Broca's statement as to the existence of 

 a true ventricular axis in the olfactory bulb, even in the rat-terriers. 



2. That the bulb is not completely but partially occluded, or in pro- 

 cess of becoming entirely so. 



3. That the cavity of the crus in some wild species, as well as the 

 domestic species, is completely closed, thereby shutting oft' all commu- 

 nication between the paracoele and the cavity of the bulb. 



4. That the acuteness of the sense of smell is not essentially depend- 

 ent upon the relative size of the rhinocoele. 



5. That atrophy is not necessarily a concomitant of occlusion. 



6. That domestication and a consequent disuse of olfaction as a means 

 for procuring sustenance may be a factor in promoting occlusion. 



DESCRIPTION OF PLATE. 



Fig. I. A transection of the dog's olfactory bulb, enlarged four diam- 

 eters. 



a. Glomerular layer. 



b. Gelatinous layer. 



c. Medullary layer. 



d. Rhinocoele divided into three smaller cavities by the growing to- 

 gether of the walls. 



The plexiform layer is present in the dog, but is not represented in 

 the diagram. Neither are the ganglionic and granular layers shown. 

 Fig. 2. A transection of the olfactory bulb of the coyote. 



e. Plexiform layer. Other letters as in fig. i . 



Fig. 3. A transection of the olfactory bulb of the dingo. 

 e. Plexiform layer. Other letters as in fig. i . 



Fig. 4. Hemi-cerebrum of a dog. Enlarged once and a half The 

 straight lines and unshaded parts represent cut surfaces. The callosum 



