424 ZOOLOGY SECT. 



occipital and the parietals is a median ossification, the inter- 

 parietal (int. pa.}, which is not one of the essential elements of 

 the vertebrate skull, but a representative of a class of bones 

 the so-called Wormian bones intercalated in certain situations 

 in the course of the sutures. The frontals are intimately united 

 along the middle line by means of the frontal suture. Laterally 

 their orbital plates form an important part of the upper portion 

 of the inner wall of the orbit; above this, over each orbit, is a 

 curved, somewhat crescentic process, the supra-orbital process, 

 Between the ali-sphenoid below, the parietal and frontal above,, 

 the frontal and orbito-sphenoid in front, and the parietal behind, 

 is a broad bone (sq.), the superior margin of which is bevelled off. 

 This is the squamosal. It gives off in front a strong zygomatic 

 process, which curves outwards, then downwards, and finally for- 

 wards, to unite with the jugal in the formation of the zygomatic 

 arch. Below the root of the process is a hollow, the glenoid fossa. 

 Behind it gives off a slender process, the post-tympanic process 

 (p. t. sq.), which becomes applied to the outer surface of the periotic. 



Between the occipital and parietal bones, below and behind the 

 squamosal, are the tympanic and periotic bones. The tympanic 

 forms the bony part of the wall of the external auditory meatus : 

 below it is dilated to form a process (ty. lid.} projecting on the 

 under surface of the skull the bulla tympani. The periotic (p. ot.) 

 is a bone of irregular shape enclosing the parts of the mem- 

 branous labyrinth of the internal ear ; externally it presents two- 

 small openings -the fenestra ovalis and fenestra rotunda, visible 

 only when the tympanic is removed; internally it bears a de- 

 pression, the ftoccular fossa, for the lodgment of the flocculus of the 

 cerebellum. The periotic and tympanic are not ankylosed together, 

 and are loosely connected with the surrounding bones, being held 

 in position by the post-tympanic processes of the squamosal. Be- 

 tween the tympanic and periotic are two foramina of importance, 

 the stylomastoid, which transmits the seventh cranial nerve, and 

 the Eustachian aperture, at which the Eustachian tube opens. 



Roofing over the ohactory cavities are two flat bones the nasals 

 (nas.) each having on its inner surface a very thin hollow process, 

 the naso-turUnal, a detached part of the ethmoid. In front of the 

 nasals are the pre-maxilla3 (p. max) large bones which form the 

 anterior part of the snout, bear the upper incisor teeth, and give 

 off three processes a nasal, a palatine (pal. p. max), and a maxillary. 

 The maxillce (max.), which form the greater part of the upper jaw, 

 and bear the pre-molar and molar teeth, are large, irregularly-shaped 

 bones, the outer surfaces of which are spongy. They give off 

 internally horizontal processes the palatine processes (pal. max) 

 which unite to form the anterior part of the bony palate. Between 

 the pre-maxilla3 and maxillae and the palatines on the lower surface 

 of the skull is a large triangular opening divided into two the 

 anterior palatine foramina by the palatine processes of the pre- 



