OSSEOUS SYSTEM. 137 



rest of the Chelonia and Crocodiles. Externally and behind the 

 intermaxillary is placed the superior maxillary bone. This bone 

 is long, and beset with teeth of equal size in the ordinary Ser- 

 pents, but very short and thick in the Venomous species, where it 

 is hollowed out posteriorly, and supports the poison-tooth or fang. 

 The lower jaw consists generally of two halves, which are com- 

 pletely anchylosed together to form a continuous arch of bone, with- 

 out any trace of suture, in the Chelonia ; in the Crocodiles and the 

 rest of the Sauria, both halves are firmly connected by suture and 

 synchondrosis ; in the Ophidia, however, they are generally per- 

 fectly loose, being connected only by an intervening membranous 

 symphysis, so that they can be separated widely from each other ; 

 indications of this separation may even be remarked externally in 

 the groove upon the integument covering the chin. By means of 

 this structure the mouth can be prodigiously expanded so that the 

 Serpents can swallow living prey of much larger bulk than them- 

 selves. Each half of the lower jaw consists regularly in the Che- 

 lonia, Crocodilia, and most other Sauria, of six bony pieces. The 

 Serpents have at least five, but the venomous kinds probably only 

 three pieces. When, however, all six pieces are present, they are 

 as follows : 1st. Most anteriorly, the large Dental piece (pars 

 alveolaris) which, with the exception of the Chelonia, supports 

 teeth. 2d. Posteriorly, the mostly small Articular piece (p. an- 

 gulans) which, either alone, or in conjunction with No. 4, forms the 

 concave joint for receiving the quadratal bone. Between these 

 two terminal pieces, the following, united together by suture, 

 and separable by maceration, are interposed, namely, 3d, the Ex- 

 ternal accessory piece (p. complementaris externa) a bony plate, 

 forming the greatest part of the external and posterior wall of the 

 inferior maxilla. 4th. The Posterior accessory piece (p. comple- 

 mentaris posterior), which is situated beneath the former, and 

 frequently concurs with the articular in forming the cavity for the 

 os quadratum. 5th. The Anterior or Internal accessory piece (p t 

 complementaris anterior), a plate of bone which assists in forming the 

 inner wall of the lower jaw, and abuts anteriorly against the dental 

 piece. 6th. The Coronoid piece (p. coronoidea), forming the highest 

 part in the middle of the lower jaw, and which obviously corresponds 

 to the coronoid process in Man and the Mammalia. 



Associated with the diversified forms of the several classes of 

 Reptilia, are many peculiar modifications in the structure of the 



