SPECIAL ANATOMY. 151 



tlie roof is formed by the frontal bones from whicli a 

 plate projects downwards to tbe upper extremity of the 

 crista galli process of tbe ethmoid bone, which forms the 

 centre of the anterior surface and on either side of which 

 are found the ethmoidal fossae (or olfactory sinuses) 

 which are bounded by the cribriform 'plate of the ethmoid, 

 while the body of the ethmoid forms the lower part of 

 the anterior surface. In forming the lateral part of the 

 walls of the cranium the parietal bones articulate with the 

 wing of the sphenoid and with the squamous temporal, and 

 the latter, in its turn, is posteriorly almost completely 

 separated by the petrous temporal bone from the occiput. 

 The floor of the cranium is formed posteriorly by the 

 basilar process of the occiput, from which the body of the 

 sphenoid runs forwards to the body of the ethmoid. 

 From, the lateral part of the body of the sphenoid the 

 alae run to articulate anteriorly with the ethmoid and 

 frontal bones, laterally with the parietal and squamous 

 temporal ; posteriorly each presents a rough margin with 

 several notches which combines with the basilar process of 

 the occiput and the temporal (petrous) bone to form the 

 foramen lacerum basis cranii. 



Foramina of the cranium. Foramen magnum, formed 

 wholly by the occiput. Affords attachment to the anterior 

 margin of the dura mater of the spinal cord and gives 

 passage to the spinal cord, which here commences from 

 the medulla oblongata, and its membranes. Also to 

 venous sinuses, the meningeal and basilar arteries, and the 

 major portion of the spinal accessory pair of nerves. 

 Forameyi condyloideum, formed by the occiput at the side 

 of foramen magnum, in front of the condyle. It gives 

 passage to the twelfth, lingual, or hypoglossal nerve. 



Foramen lacerum basis cranii, situated at the side of the 

 basilar process of the occiput, formed by the occipital, 

 sphenoid, and petrous temporal bones. In the human sub- 

 ject by a bony septum is divided into two parts (in the 

 horse by a ligament) ; through the posterior run the glosso- 

 pharyngeal, pneumogastric, and spinal accessory nerves ; 

 through the anterior, the inferior maxillary division of the 

 fifth, internal carotid artery, and meningeal branches, and 

 a dilated vein running from the cavernous sinus to the 

 jugular at its commencement. 



Foramen auditorium internum. A circular opening at 



