978 



CIIKI.OXIA. 



CHKI.ONIA. 



: -.1 



pUo in the frame of the orbit, in articulated also, u ordinarily, U> 

 the ante-orbital apophyais of the maxillary bone, descend* within the 

 nrt.it, form* the anterior aeptuni, which separates the orbit from the 

 nose, and i* articulated below with the palatine and the vomer, 

 leaving between it, the maxillary, and the palatine, an oblong hole, 

 which lead* into the posterior nostrils. The osseous cavity of the 

 noee is oblong, and formed by the maxillaries, the intermaxillariu*, 

 the voiner, the two anterior and the two principal frontal*. The 

 Xtaot of the anterior frontal* and the absence of the luutal bones are 

 the cause* that the first articulate with each other, and that they 

 extend above the orbit and outaide the principal frontal* up to the 

 posterior frontal* in Trthtdo liulita, or very near it in some other 

 species. The intcrmaxillaries have no ascending apophysis. They 

 form, as ordinarily, the termination of the muzzle, and are directed 

 backward* in the palate between the maxillaries, and even between 

 the posterior nostrils, to the vomer. The poitterior nostrils are two 

 large aperture* pierced on each side in the middle of the nasal cavity 

 between the maxillaries, the intermaxillaries, the Tomer, and tlie 

 anterior frontal bones. The bottom of the cavity of the nose is 

 covered above and closed behind by the principal frontals, which 

 leave a large aperture between them, closed by a cartilage which 

 permits the passage of the filaments of the olfactory nerve. Lower 

 and laterally there is, between the frontal, the anterior frontal, and 

 the vomer, a rather large space closed by a continuation of the same 

 cartilage, which represents the os planum. In the Terrestrial 

 Tortoise there is no inter-orbital simple cartilaginous septum, or 

 nearly none ; but this is not so in other sub-genera. The frontals 

 cover but very little of the cerebral chamber, because they are short, 

 and together form a lozenge wider than it is long. The parietals 

 form together a |>entagon, the most acute angle of which proceeds to 

 unite itself with the occipital spine. They cover more than half of 

 the cerebral chamber, and are directed backwards by means of a 

 scaly suture on the occipital bone and on the petrous bone. On each 

 side the parietal bone descends very low into the temporal fossa; 

 there it occupies nearly all the space which the temporal wing of the 

 sphenoid bone occupies in the crocodile, and in the tortoise there 

 only remains a very small portion of this bone, which unites on one 

 aide to the descending portion of the parietal ; on the other to the 

 palatine, the internal pterygoid, the body of the sphenoid, the 

 tympanic cavity, and the os petrosum. The jugal bone is articulated, 

 as ordinarily, with the external and posterior angle of the maxillary 

 bone. It is narrow and continued under the orbit, behind which it 

 encounters the posterior frontal bone, which completes the frame in 

 this part, and the squamous portion of the temporal bone, which 

 forms by itself the whole zygomatic arch, as may be seen in many of 

 the C'elaeta. The temporal bone widens to unite itself to the 

 tympanic cavity, which is extremely large. It forms a frame which 

 i* nearly completely bony for a large tympanum ; and below this 

 frame it descends in form of an apophysis for the articulation of the 

 lower jaw. This frame lead* into a vast cavity, completed only at 

 its upper posterior angle by the mastoidean. At the bottom of this 

 cavity in a hole through which passes the ossiciilum auditus to arrive 

 at a second cavity, formed externally by the bone of the tympanic 

 cavity, on the internal side by the petrous bone and the occipital 

 bones, below a little by the sphenoid bone, and closed backward* by 

 cartilage. It is a second part of the tympanic cavity which in tlm 

 divided by a constriction, of which we have examples among the 

 mammals, especially in the genus Petit, but the communication 

 between the two parts is less narrowed than in the Tortoise. The 

 tympanic bone forms besides a considerable part of the posterior 

 wall* of the temporal fossa. Between it and the parietal the petrous 

 bone show* itself in this same temporal fossa, and the cranium is 

 dosed behind by the occipital bone, which is here divided into six 

 bones, not into four ; for the lateral occipital* are each divided into 

 two |*rts, the most external of which Cuvier terms the exterior 

 occipital. The fenestra ovalis is, he observes, common to the petrous 

 ixme and this exterior occipital ; as, in the crocodile, it is common to 

 le petrous bone and the ordinary lateral occipital: the fenestra 

 tunda, on the contrary, i pierced in the exterior occipital, as it is 

 1 in the lateral occipital of the crocodile. The two bones 



ibute to the formation of the cell of the labyrinth with the 



upper occipital as the petrous bone and the lateral occipital aoMri 



in the crocodile. In both genera the great aperture for 



the fifth pair of nerve. i in front of the petrous bone, 



wtween it and the temporal ala. In the Turtle this hole is between 



le petrous bone and the descending part of the parietal bone. The 



" i* simple, as in the crocodile, and formed of a 



er stem which widens at the point of it* approximation to the 



itraovmli*, and which is there applied by a round and concave 



so that t has nearly the figure of a trumpet. The 



ihuui tibe is entirely cartilaginous or membranous. It 



nmences in the external chamber of the cavity, above, by a large 



notch of the posterior hordcr of the tympanic !..,',., near the edge of 



' tympanum itself, and is directed obliquely within, pr.wing 



bone of the cavity and the depressor muscle of the 



lower jaw, to a notch of the lateral and posterior Iwrdcr of th. 



pUrygoid bone, whereby it penetrates into the back of the fauces, on 



ide, close to the articulation of the lower jaw, but far enough 



from iU congener, and e|wcmlly very far behind the intcnial nostrils. 

 On the palate, or rather, behind the roof of the back of the mouth, 

 may be seen the orifiow of two tul.cn, under the form of two umall 

 hole* separated from each other. 



Kkllll <if TfMlutla Inilira. 

 I, Profllp; 2, neon from above; 3, Keen from below ; 4, wen from behind. 



Reverting to the lower .-inl'.M.- of tl,<> cMiiinni, l.chind the 

 maxillaries ami the frontals, posterior to the two widen of the vom.-r. 



