MUSi:UM OF COMPAKATIVE ZOOLOGY. 145 



sketch tliG general |)lan of arrangement of the ethmoid bone in the 

 mammals, and to indicate the relations that the several parts hold one 

 to another. Before describing the bono in the Cheiroptera, I propose 

 giving detailed accounts of the ethmoid in the cat, the seal, the peccar}-, 

 the sloth, and the mole ; with the object of bringing together some 

 widely diverse examples, and ])resentiug descriptions which will be sufli- 

 cientlv detailed to permit of comparisons being made witli those which 

 will follow in tlic concluding portion of tliis ])aper. 



In tlie horse (Plate II. figs. 4, 5) the endoturbinal aspect of the encra- 

 nial surface is concealed from the brain case at its upper third by a trans- 

 verse plate apparently of the frontal bone, but which in reality is an 

 ossification of the ethmoid. The foramina of the endoturbinal surface 

 ai'C arranged elaborately in a crescent extending across the anterior end. 

 The foramina of the ectoturbiual surface are seen in five transverse 

 triangular or clavate clusters. 



The ethmoid, studied from its lateral aspect, exhibits a trenchant dis- 

 tinction between the endoturbinals and the ectoturbinals by a thin sep- 

 tum extending across the great crauio-facial sinus. Both the turbinal 

 sets lie in this sinus, connected by a thin papyraceous lamina, save at the 

 anterior fourth of the ectoturbiual series, wliere it is firmly connected 

 by the ends of tlie olfactoiy ])latcs to the descending process of the fron- 

 tal hone, as well as with the line of junction this process effects with the 

 orbitosphenoid and the frontal bones. 



Seen in transverse section, the turbinal mass exhibits sharply the di- 

 vision between the two sets of plates. The ectoturbinals are eight in 

 number, including the nasoturbinal. The endoturlnnals are five in num- 

 ber, and preserve the order already described as existing in the hog. 

 The last plate sends backward a single folium within the sphenoidal sinus, 

 so that tlie olfactory apparatus extends a short distance posterior to tlie 

 encranial surface. 



Seen from the median aspect, the nasoturbinal is seen to assume 

 enormous proj^ortions, being much wider than any of the endoturbinals. 

 Four of the endoturbinals are visil)le, and all are markedly biconvolute, 

 the convexities of the scrolls alune appearing on the general surface. 

 Anteriorly each plate is seen ending siuijily at the bases, Imt toward 

 the apices they arc more or less lohate. 'JMie first and second plates 

 project beyond the transverse lamina. 



A small lint distini't plate crosses the septoturbinal sjiace obliquely at 

 the orifice of the sphenoid sinus. The septum is distinctly foliated 

 opposite the third, foui-th, and fifth ])lates. 



vol.. X. — NO. :'.. 10 



