XIII 



PHYLUM CHORDATA 425 



maxilla?. On the outer surface of each maxilla 1 , above the fii->i 

 pre-molar tooth, is a foramen the Infra-orbital through which 

 the second division of the fifth nerve passes. A strong proc< 

 which is given off from the outer face of each maxilla and turns 

 outwards and then backwards to unite with the zygomatic proct->s 

 of the squamosal and thus complete the zygomatic arch, is a 

 separate bone in the young, the malar or jugal (ju.*). 



The maxillae help to bound the nasal cavities externally, and each 

 gives off on its inner aspect a pair of thin scroll-like bones the 

 niaxillo-turbinals, which, like the naso-turbinals, are separated 

 portions of the ethmoid. The rest of the narrow bony palate, 

 forming the roof of the mouth and the floor of the nasal cavities, 

 is formed by the palatine plates of the palatine bones (pal.}. The 

 pterygoids (p.) are small irregular bones, each of which articulates 

 with the palatine in front and with the pterygoid process of the 

 alisphenoid behind. The lacrijmals (kr.) are small bones, one 

 situated in the anterior wall of each orbit, perforated by a small 

 aperture the lacrymal foramen. 



In the interior of the skull are three cavities, the two olfactory 

 or nasal cavities, right and left, in front, and the cranial cavity 

 behind. The former are separated from one another by a median 

 partition or septum, partly bony, partly cartilaginous, formed, as 

 above described, by the mesethmoid. Each contains the turbinals 

 or turbinated bones of its side ; it opens on the exterior by the 

 large external nasal aperture, and behind it communicates with the 

 cavity of the mouth by the posterior nasal aperture. 



The cranial cavity has its walls moulded to a considerable extent 

 on the surface of the contained brain, and, in consequence, there 

 are to be recognised concavities in the former corresponding with 

 the prominent portions of the latter. These concavities are termed 

 the fossce, and they consist of the cercbellar fossa behind and the 

 cerebral fossa in front, with the inconspicuous olfactory fossa in the 

 frontal region. 



The mandible., or lower jaw, consists of two lateral halves or rarni, 

 which articulate with one another in front by a rough articular- 

 surface or sympliysis, while behind they diverge like the limbs of a 

 letter V. In each ramus is a horizontal portion (anterior) which 

 bears the teeth, and a vertical or ascending portion, which bears 

 the articular surface or condijle (cond.) for articulation with the 

 glenoid cavity of the squamosal ; in front of the condyle is the 

 compressed cwonoid. process. The angle where the horizontal and 

 ascending processes meet gives off an inward projection or angular 

 process (ang. pro.). 



The hyoid consists, in addition to the separate vestigial stylo- 

 hyals already mentioned (p. 422), of a stout thick body or basi-hyal, 

 a pair of small anterior cornua or cerato-hyals, and a pair of long 

 backwardly directed cornua or thyro-hyals. 



The auditory ossicles, contained in the cavity of the middle ear, 



