28 BONES OF THE HEAD. 



the carotid artery and the ganglion of Laumonier. Upon the septunri 

 between the jugular fossa and carotid canal, is the entrance to the 

 aqueduct of the cochlea. 



The anterior surface presents a groove leading to a foramen 

 called hiatus Fallopii, which transmits the superficial petrous nerve, a 

 branch of the vidian ; behind this is the eminentia arcuata, made by 

 the prominence of the labyrinth. At the edge is a groove for the 

 superior petrosal sinus, and near the apex a semilunar depression 

 for the ganglion of Casser. 



The posterior surface has a large opening near the middle, in- 

 ternal meatus auditorius ; it is not deep, and the base is cribriform. 

 Immediately above it, is a foramen or fissure for the dura mater and 

 a small vessel ; behind it is a ridge produced by the inferior semi- 

 circular canal, and half an inch behind it is the aqueduct of the 

 vestibule, concealed by an osseous lamella. 



ETHMOID. 



Is SO called from its resemblance to a sieve. It is placed in the 

 median line, at the base of the skull, in front of the sphenoid bone, 

 and between the orbitar processes of the frontal. Is cuboidal in 

 shape and cellular in structure. 



The siiperio7' surface is called the cribrifoj-m j^lnte* which is per- 

 forated with holes for the transmission of filaments of the olfactory 

 nerve ; the most anterior hole is the largest, and transmits the internal 

 nasal nerve. From the median line is a narrow, triangular, hollow 

 process called the crista galli^ and to it is attached the falx cerebri. 

 In front of this is sometimes the foramen or groove called foramen 

 crecum, which admits of the passage of a small vein from the nose. 



The bone is divided longitudinal iy into two halves by the vertical 

 plate of bone called the 'yiasal lamella ;'^ this can best be seen by ex- 

 amining the inferior surface. It articulates below with the vomer, 

 and behind with the crista sphenoidalis. 



The lateral surfaces of the bone are called the ossa plana.^ The 

 Pig 13 OS planum is extremely thin and papy- 



raceous, forming a large part of the 

 orbit of the eye. On its upper edge are 

 two grooves, which are converted into 

 two foramina, called internal orbit ary 

 or ethmoidal ; the anterior transmits an 

 artery, vein, and the internal nasal 

 nerve; and the posterior transmits an 

 artery and vein. The inferior edge 

 articulates with the superior maxillary 

 bone. When the bone is viewed from 

 behind, there will be seen two scrolls or 

 shells On either side of the nasal la- 



