378 SKELETON OF THE FOWL 



a membrane-bone which forms part of the 

 boundaries of the tjTnpanie cavities, and pro- 

 bably corresponds to the posterior part of the 

 para-sphenoid of the frog. 



In front of the basi-temporal, the base of 

 the skull is narrow, and formed by the ros- 

 trum, or thickened ventral border of the inter- 

 orbital septum. 



ii. The anterior openings of the Eustachian tubes 

 are a pair of small holes, close to the median 

 plane, and opening into a deep notch between 

 the anterior end of the basi-temporal bone and 

 the rostrum. 



iii. The foramina of exit for the carotid canals 

 are a pair of small holes, near the middle line, 

 and immediately to the outer sides of the 

 Eustachian apertures. They are connected 

 with each other by a canal, traversing the 

 base of the skull. 



Pass a bristle along the carotid canal of one side, and 

 through the transverse canal from side to side. 



0. The side of the cranium. 



i. The tjrmpanic cavity is a hemispherical depres- 

 sion, at the side of the hinder end of the skull, 

 bounded above by the squamosal and below by 

 the hasi-temporal. The tympanic membrane 

 is attached just within its prominent lip. 



Within the tympanic cavity can be seen 

 the following. 



H. The fenestral recess is an oval depression in 

 the middle of the cup, divided by a parti- 

 tion into an upper hole, the fenestra ovalis,. 

 and a lower, the fenestra rotunda. The 

 former of these lodges during life the inner 

 end of the auditory ossicle, or columella, a 

 slender bar of bone and cartilage, the outer 



