454 ZOOLOGY sect. 



bones, one situated in the anterior wall of each orbit and perforated 

 by a small aperture — the lacrymal foramen. 



In the interior of the skull (Fig. 1083) 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 cartilaginous, partly bony, 

 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 



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p.sph 



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ar.oc 



Flo. 10S3.— IiepuB cuniculus. Skull in longitudinal vertical section. The cartilaginous 

 nasal septum is removed, a. sph, alisphenoid ; e. oc. exoccipital ; e. th. ethmo-turbinal ; 

 eth. ethmoid ; Jt. fossa for flocculus of brain ; i. incisors ; mx th. maxillary turbinal ; ii. ih. 

 naso-turbinal ; jiaV. palatine portion of the bony palate ; peri, periotic (petrous portion) ; 

 p. sph. presphenoid ; sph. f. sphenoidal fissure ; st. sella turcica, or depi-ession in which the 

 pituitary body lies ; I. point <at which the' olfactory nerves leave the skull ; II. optic 

 foramen; Vm?t. foramen for mandibular division of trigeminal ; VII. for facial nerve; 

 VIII. for auditory nerve ; IX, X, XI, for glossopharyngeal, vagus, and spinal accessory ; XII. 

 for hypoglossal. Other letters as in Fig. 1082. (From Parker's Practical Zoologi/.) 



are to be recognised concavities in the former corresponding with 

 the prominent portions of the latter. These concavities are termed 

 the fossm, and they consist of the cerebellar 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 rami, 

 which are connected with one another in front by a rough articular 

 surface or symphysis, 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 condyle {cond.) for articulation with the 

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

 compressed coronoid process. The angle where the horizontal and 

 ascending processes meet gives off an inward projection or angular 

 process {any, pro.). 



