876 SKULL 



of smaller foramina for the exit of tlie 1st branch of the ne,rv. 

 trigeminus and of the 3rd, 4th and 6th Cranial Nerves. Frequently, 

 however, one or more of these leave the cranial cavity together 

 with the optic nerve, converting in such cases the optic foramen 

 into a foramen lacerum anterius. The olfactory or 1st pair of 

 cranial nerves leave the cranial cavity at the point where the 

 Orbitosphenoid meets the Frontal, and reach the nasal cavities 

 by passing above the interorbital septum. 



The Frontals form the greater portion of the upper surface of 

 the Skull, and by their forward, lateral or backward expansion 

 come into contact with a great number of bones, such as the 

 Parietals, Squamosal and Opisthotic, Ali-orbitosphenoid, Ethmoid, 

 Lacrymal and Nasal, Maxillary and Prsemaxillary. In most em- 

 bryos the Frontals and Nasals are originally separated by the 

 upper portion of the Ethmoid, which appears on the surface, and 

 this condition is persistent in Struthio ; but otherwise the Ethmoid 

 is overlaid by expanding growths of the Prsemaxillae and the Nasals 

 until these reach the Frontals. Posteriorly the Frontals combine 

 with the Squamosal and Alisphenoid in forming the postorbital 

 process ; and, as this part often ossifies from a separate centre, it 

 possibly represents the postfrontal of other Vertebrates. The space 

 between the Frontal, Orbitosphenoid and Ethmoid is filled by the 

 Lacrymal, which always forms part of the anterior border of the 

 orbit ijprocessus orbitalis anterior), and has a perforation through 

 which pass the secretions of the lacrymal and various orbital glands. 

 The Lacrymal exhibits many modifications which seem to be of some 

 taxonomic value : most generally it fuses with the Frontal and 

 Nasal, but it may fuse with the former and articulate with the 

 latter, or vice versa as in Vanellus ; or it may articulate with both as 

 in Ardea, or may fuse with the much- expanded Maxilla, as in 

 Balseniceps and Podargus ; or it may fuse with the Ethmoid as in 

 Corvus corax, or again may articulate with the Palatal as in 

 Struthio, or with the Jugal as in Corvus, Psittaci and Accipitres. 

 Many birds, as most Accipitres, several Gallinx, beside Grus and 

 Struthio, possess Supraorbital bones which are loosely attached, one 

 or more on either side, to the posterior margin of the Lacrymal and 

 the adjoining side of the Frontal. To the same category as these 

 belong the Infraorbitals, which join the Jugal or downward process 

 of the Lacrymal, and protect the lower side of the eyeball. 



The Nasals, which are always conspicuous, send out three 

 processes — (1) a jDrsemaxillary which joins laterally the posterior 

 dorsal praemaxillary process and forms the upper margin of the 

 nasal cavity, (2) a lateral one, descending and joining the Maxilla 

 so as to border the nasal cavity behind, and (3) a frontal process 

 which, uniting with its fellow on the other side, overlaps the upper 

 surface of the Ethmoid and frequently fuses Avith the anterior 



