326 VERTEBRATE ZOOLOGY 



posteriorly) and a transverse position, and has at its base three 

 small round holes in a transverse row which separate it from the 

 remainder of the alisphenoid. These holes, of which the anterior 

 and medial one is much the largest, are the three sphenoidal foram- 

 ina, and furnish a passage for a part of the mandibular branch 

 of the trigeminal nerve and also for an artery. Just in front of the 

 tympanic bulla is the large, irregular foramen lacerum, for the 

 passage of a part of the mandibular nerve and also an artery. 



In front of the basisphenoid in the midventral area is the slender 

 presphenoid bone ; it will be seen with difficulty in a ventral aspect 

 because it lies between the two nearly vertical palatine bones. 

 The narrow space between these bones incloses the nasopharynx, 

 the hinder part of the nasal cavity ; it will be seen that the palatine 

 separates the nasopharynx from the orbit. Extending dorsally 

 from the side of the presphenoid is the wing, or orbitosphenoid, 

 which forms the middle portion of the wall of the orbit and incloses 

 the large round optic foramen, through which the optic nerve 

 enters the orbit from the cranial cavity. Ventral to this foramen 

 is the large slitlike orbital fissure, through which the oculomotor, 

 trochlear, abducens, and the ophthalmic and maxillary branches 

 of the trigeminal nerves enter the orbit. 



The palatine bone, on each side, extends ventrally from the 

 presphenoid and forms, as shown above, the side of the naso- 

 pharynx and also the lower wall of the orbit. Note that it abuts 

 the orbitosphenoid and the pterygoid process of the alisphenoid 

 and with them forms a large part of the wall of the orbit. An- 

 teriorly the palatine abuts the maxillary bone and with it forms 

 the hard palate of the roof of the mouth and also a portion of the 

 floor of the nasal cavity. Directly behind the hard palate are the 

 internal nares, or choanae, the opening of the nasal cavity into 

 the nasopharynx. The hard palate forms a bridge here which 

 joins the right and left sides of the upper jaw between the grinders. 

 In front of the palatal bridge is the pair of very long incisive 

 foramina, which separate the right and left sides of the upper jaw 

 from each other and which open into the nasal cavities. Note the 

 suture between the maxillary and intermaxillary bones, and the 

 long palatal process of the intermaxillaries in the median area. 



