MUSEUM OF COMPARATIVE ZOOLOGY. 141 



separating them is distinctly ridged, and is conspicuous in the raccoon 

 and the dog, but inconspicuous in the sloth. This ridge is the basal en- 

 cranial aspect of the first endoturbinal, and the foramina ranged on the 

 sides and at the tip of the ridge afford openings of exit to the olfactory 

 nerves supplying the sides of the plate. Indeed, all the olfactory nerves 

 excepting those of the septoturbinal spaces are similarly placed with 

 respect to basal lines of the ethmoturbinal plates. The first endoturbi- 

 nal, being the largest of the series, secures for its base a more decided 

 line than is the case with the others. The septal openings are arranged 

 in a single straight line parallel to the crista galli. 



The simplest arrangement of foramina is seen when a row of openings 

 lies parallel to the median border of the encranial surface, and another 

 is seen similarly disposed along the lateral border. The successive de- 

 gi-ees of complication on the surface are dependent upon the extent that 

 the basal ridges extend medianly from the last-named row. 



A general idea of the plan of the ethmoidal plates can be thus formed 

 by the study of the encranial surface. The number of the foramina 

 present, the size of the basal ridges, the extent of the non-perforate 

 space, will be found to hold an exact relation to the number and size of 

 the olfactory plates, and indirectly to the functional importance of the 

 olfactory region. 



As a rule, the encranial ectoturbinal surface is rounded in form, and 

 of greater diameter than the surface for the endoturbinals. In the cat 

 the cribriform plate is everywhere narrow, the ectoturbinal surfaces be- 

 ing separated by a median frontal process, on either side of which septal 

 foramina are arranged. The crista galli is not developed at the anterior 

 third of the endoturbinal region. The ridge for the first endoturbinal is 

 scarcely longer than the width of the septoturbinal space at its side. 

 The second endoturbinal closely resembles the first. The foramina of 

 the last-named plates are continuous at the lateral border of the cribri- 

 form plate. The ridge of the third plate is indeterminate, the foramina 

 being large and clustered. 



In the dog (Plate I. figs. 1, 2) the ectoturbinal surface is subrounded, 

 higher than it is broad, with the septoturbinal space widened superiorly. 

 The ectoturbinal ridges and foramina are displayed laterally, and lie on 

 the level of the descending portion of that portion of the frontal bone 

 articulating with the orbitosphenoid. The first endoturbinal ridg 

 three times the width of the related Beptoturbinal space. The second 

 is tw.. thirds the length of the first. The third ridge is. as'in the 

 indeterminate, and the foramina are clustered 



