xin PHYLUM CHORDATA 389 



which is firmly united to the other cranial bones. The main part 

 of the auditory capsule is ossified by a large pro-otic (Fig. 1031, 

 PR. OT) : the small opisthotic of the embryo early unites with the 

 exoccipital, the epiotic with the supraoccipital. The presphenoid 

 and mesethmoid together form the interorbital septum (Fig. 1030, 

 i.o.s.), a vertical partition, partly bony, partly cartilaginous, which 

 separates the orbits from one another. It is very characteristic of 

 the Bird's skull that the immense size of the eyes has produced 

 a compression of this region of the skull. The ecto-ethmoids or 

 turbinals are comparatively poorly developed, in correspondence 

 with the small size of the olfactory organs. There are large 



AL.SPH 



J>A 



Fin. 1031. Sagittal section of a Bird '8 skull (diagrammatic). Replacing bones AXi.SFH. alisphe- 

 noid; ART. articular ; B.OC. basioccipital ; B.SPH. basisphenoid ; EP.OT. epiotic; 

 EX.OC. exoccipital; 1VI.ETH. mesethmoid; OP.OT. opisthotic ; ORB.SPH. orbito- 

 sphenoid ; PR.OT. pro-otic ; QU. quadrate ; S.OC. supraoccipital. Investing bones 

 ANG. angular; B. I'M P. basi- temporal ; COR. coronary; DNT. dentary ; FR. frontal ; JU. 

 jugal ; LCR. lacrymal ; MX. maxilla ; NA. nasal ; PA. parietal ; PAL. palatine ; PMX. pre- 

 maxilla; PTG. pterygoid ; QU. JU. quadrate- jugal ; RS T. rostrum ; S. ANG. supra-angular; 

 SPL. splenial ; SQ. squamosal ; VO. vomer. fie. fos. floccular fossa; nix. pal. pr. rnaxillo 

 palatine process ; opt. for. optic foramen ; orb. pr. orbital process ; ot. pr. otic process ; 

 pty.fos. pituitary fossa. 



lacrymals (Fig. 1030, lc. t Fig. 1031, LOR), and the nasals (na, na', 

 na", NA) are forked bones each furnishing both an inner and an 

 outer boundary to the corresponding nostril. 



The premaxillse (p.mx., PMX) are united into a large triradiate 

 bone which forms practically the whole of the upper beak. The 

 maxillae (mx., MX), on the other hand, are small, and have their 

 anterior ends produced inwards into spongy maxillo- palatine pro- 

 cesses (Wig. 1030, mx.p., Fig. 1031, mx.pal.pr). The slender posterior 

 end of the maxilla is continued backwards by an equally slender 

 jugal (ju., JU) and quadra to-jugal (QU. JU) to the quadrate. 

 The latter (qu., QU.) is a stout, three-rayed bone articulating by two 

 facets on its otic process (ot. pr.) with the roof of the tympanic 



VOL. II B B 



