REPTILES. 



jaw is uninterrupted, and correfponds to the curve ot the 

 lower ; the concavity ot the palate is nearly complete in 

 front. The palatine arches are dircdled backwards, and 

 united to the condyloid pedicle of the temporal bone. This 

 pedicle is Ihort, and nearly vertical, and excavated behind 

 for the attachment of the digallric mufcle. The lower jaw 

 has a fm-j.ll procefs behind its articulation for the attachment 

 of the mufcles, whicli deprefs it ; and another towards its 

 polterior third portion, analogous to the coronoid, for the 

 elevating mufcles. 



In the amphifbxna, although the general configuration is 

 a little changed, nearly the fame arrangement is met with. 

 The whole upper jaw is lefs feparated from the cranium ; 

 the concavity of the palate is nearly complete. The pala- 

 tine arches are much larger. The condyloid pedicle of the 

 temporal bone, inllead of being vertical, is continued nearly 

 horizontally forwards. In proportion to the cranium, the 

 lower jaw is much (horter ; and it is articulated to the con- 

 dyle by its pofterior extremity. It is very wide behind, to 

 produce the coronoid procefs. The orbit and temporal 

 folfa are completely confounded ; they are bounded by pro- 

 minent bony criftse, as in the carnivorous mammalia ; hence, 

 on tirft view, the head of an amphifljina might be fuppofcd 

 to belong to one of the cheiroptera. 



The ierpents of the fecond kind, whofe lower jaw is 

 formed of two diftinft branches, and in which the upper 

 is capable of being feparated, but not carried forwards, are 

 all the non-venomous colubres, and the boas. The con- 

 formation of the upper jaw, in the latter, is very different 

 from that of the lizards, although the bones are nearly the 

 fame, as we fhall explain in the olleology of the head. The 

 offa incifiva are not always furnilhed with teeth ; fometimes 

 even, as in the boas, they do not unite tlie fuperior maxil- 

 lary bones. All the other bones of tlie jaw are moveable on 

 the cranium, which ferves merely as a point of fupport. 



The fuperior maxillary bones are two long branches, in 

 which the teeth are implanted ; they form the outer edge 

 of the palate. They are articulated by two points ; firit 

 towards their middle, as a lever of the firft kind, on a fmall 

 bone analogous to the os make, and forming the anterior 

 edge of the orbit : nearly at the fame point, but towards 

 the inner fide, the fuperior maxillary bone has a procefs, 

 which Aides in a groove, and refts on the palatine arch. It 

 moves on thefe two furfaces, playing backwards and for- 

 wards. The anterior extremity of this upper maxillary bone 

 is free : the pofterior receives the end of a particular bone, 

 ferving to unite it to the palatine arches. 



The palatine arches arc the two internal bony branches 

 themfelves, formed of two parts. An anterior, which is 

 free in front, and articulated by three points ; behind, with 

 a bony branch, which proceeds towards the extremity of the 

 lower jaw within its articulation, and appears to form a 

 continuation of it ; on the outfide, with a particular bone, 

 uniting it to the maxillary arch ; and above, with the bafis 

 of the cranium, in front of the orbits. The pofterior por- 

 tion of the palatine arch is analogous to the pterygoid 

 aliE or laminx. It is articulated by three points; ift, 

 in front, with the pofterior extremity of the iirft portion ; 

 2d, behind, with the lower jaw towards the infide ; 3d, on 

 the outfide, and towards its anterior part, with the bone 

 uniting it to the maxillary arch. Laftly, the third pa- 

 lato-maxillary is a piece nearly cylindrical in its middle, 

 flattened and widened at its two extremities, by which it 

 is fupported, being articulated, on the outfide, to the pof- 

 terior extremity of the maxillary arch, on the infide, to- 

 wards the middle and outfide of the pterygoid portion of 

 the palatine arch. 



In coiilequciice of this fmgular torination, the whole 

 upper jaw is, as it were, fufpended and diftinft from tlie 

 cranium, and influenced by the motions of the lower jaw. 

 When the pofterior extremities of the latter are feparated, 

 the pterygoid arches are moved apart. They carry with tiiem 

 the pofterior extremities of the palatine and maxillary arches, 

 while at the fame time the anterior extremity is moved in- 

 wards. On the contrary, when the two internal edges of 

 the pterygoid lamiux are brought togctiier, or, what is the 

 fame, when tlie articular extremities of the lower jaw tend 

 to approximate, the anterior ends of the palatine and 

 maxillary arches are carried outwards, and feparate from 

 each other. 



The ferpents of the third order, which have jaws fuf- 

 ccptible of feparation, and which at the fame time can carry 

 forwards the fuperior maxillary booes, properly fo called, 

 exhibit but a flight modification of the llruiftiire defcribed 

 as belonging to tlie preceding divifiou. Their pterygoid 

 arches are articulated with the lower jaw, toward.! its ex- 

 tremity, on the guttural afpeft. They alfo receive the 

 bone which is to join them to tlie palatine arches ; but the 

 latter are very fhort, direftcd forwards, and only containing 

 venomous teeth. Tliis intermediate bone, therefore, goes 

 above the fuperior maxillary, which is itfelf articulated in 

 the front of the orbit, or the fhort and moveable cheek- 

 bone. When the lower jaw is moved forwards, the pala- 

 tine arch, carried in the fame direftion, drives before it the 

 bone which joins it to the maxillary. The latter, extremely 

 moveable, is immediately turned up, or carried forwards, by 

 moving on the cheek-bone, which caufes a complicated 

 feries of motions. 



The articulation of the lower jaw is the fame in the whole 

 family. The temporal proceffes are prolonged pofteriorly : 

 they receive an intermediate bone ; analogous to that defig- 

 nated by the name quadratum in birds. This bone is very 

 fhort, and pofTefTes little motion, in the fpecies which have 

 the upper jaw fixed, and the inferior confolidated. 



It is direfted forwards in the amphifbxna towards the 

 lower jaw, which is fhorter than the cranium by nearly one- 

 third ; — a circumilance which belongs only to this fpecies. 

 In the anguis, the os quadratum defcends much more ob- 

 liquely forwards. 



In all the other fpecies the bone laft-mentioned is much 

 longer. It fometimes defcends perpendicularly, as in the 

 boas ; but it is commonly direfted backwards, as in moft of 

 the colubres. The temporal extremity is generally widened 

 and excavated by a fmall depreflion. The inferior extre- 

 mity is rounded hke a condyle, and received into an exca- 

 vation of the pofterior extremity of the correfponding 

 branch of the inferior maxillary bone. 



From the nature of its articulation, the lower jaw of either 

 fide is not only fulceptible of elevation and depreflion, fo as 

 to open and ihut u.e mouth, by playing on the 03 qua- 

 dratum, as is the cafe only in the genera amphifbsna and an- 

 guis ; but it may alfo be carried outwards, and take with 

 it the OS quadratum, as is the cafe in the colubres and 

 venomous ferpents, whenever the pterygoid arch is moved 

 outwards. That is to fay, whenever the upper jaw is 

 widened, the inferior mufl follow its dilatati.in, becaufe the 

 pofterior extremities of the pterygoid arches, being arti- 

 culated with the internal part of the lower jaw, it mull 

 move together with them. The arrangemeni of the mufcles 

 accords very well with this formation, as we Ihall proceed 

 to defcribe. 



Mufcies of the Jaius. — The maxillary mufcles of the 

 genera anguis and amphifbiena, and probably of all the fer- 

 pents with a confolidated under jaw, relemble ihofc of the 



commou 



