10 ELEMENTARY SKETCH OF THE, OSTEOLOGY OF BIRIJS. 



which are wedged in between the primary elements of the two, 

 segments. In front of the frontal segment we have an incom- 

 plete segment, comprehending the bones related to the nasal 

 cavity. 



Below the basi-cranial axis (the long horizontal line in the dia^ 

 gram) we have other bones which form the palatal and adjacent 

 regions of the skull. These bones do not, like those above the axis, 

 enclose a tubular nervous cavity, and are consequently not so 

 easily divided into segments. The table shows their relations 

 to the superior bones. Posteriorly these bones form two 

 arches — the hj'-oidean, and the mandibular ; the latter com- 

 mences with the quadrate, and then continues with the elements of 

 the mandible which are bent so as to be directed forwards. 

 From the base of this latter arch (quadrate) there arises another 

 chain or arcade of bones, which is directed forwards, and which 

 comprehends the quadrato-jugal, jugal, maxilla, and lachrymal. 

 Above this arcade, and below the basi-cranial axis, are in- 

 terposed the chain of the pterygoids, palatines and premaxillge. 

 The latter are in close connection with the vomer, and sq with 

 the nasal bones. 



