4O2 MANUAL OF ZOOLOGY. 



i) described by Sir William Jardine in his classical work 

 on the "Ichnology" of Annandale in Dumfriesshire. The ear- 

 liest unequivocal remains of Chelonians are in the Oolitic 

 Rocks (the Chelonia planiceps of the Portland Stone). Fossil 

 Chdoniidce, Emydidcz, and Trionyddce occur, also, from the 

 Upper Oolites to the present day, the Eocene period being 

 peculiarly rich in their remains. In the Tertiary deposits of 

 India (Sivalik Hills) there occurs a gigantic fossil Tortoise 

 the ColossocMys Atlas which is believed to have been eighteen 

 to twenty feet in length, and to have possibly survived to 

 within the human period. 



ORDER II. OPHIDI^. The second order of Reptiles is 

 that of the Ophidia, comprising the Snakes and Serpents, and 

 distinguished by the following characters : 



The body is always more or less elongated, cylindrical, and 

 worm-like, and whilst possessing a covering of horny scales, is 

 always unprovided with a bony exoskeleton. The dorsal ver- 

 tebrae are concave in front (proccelous), with rudimentary trans- 

 verse processes. There is never any sternum, nor pectoral 

 arch, nor fore-limbs, nor sacrum, and as a rule there are no 

 traces of hind-limbs. Rudimentary hind-limbs, however, are 

 occasionally present (e.g., in Python and Tortrix). There are 

 always numerous ribs. The two halves or rami of the lower 

 jaw are composed of several pieces, and the rami are united 

 anteriorly by ligaments and muscles only, and not by cartilage 

 or suture. The lower jaw further articulates with the skull by 

 means of a quadrate bone (fig. 153, a\ which is always more 

 or less movable, and is in turn united with the squamous por- 

 tion of the temporal bone, which is also movable, and is not 

 firmly united with the skull. Hooked conical teeth are always 

 present, but they are never lodged in distinct sockets or alveoli. 

 Functionally, they are capable of performing nothing more 

 than merely holding the prey fast, and the Snakes are provided 

 with no genuine masticatory apparatus. The heart has three 

 chambers, two auricles and a ventricle, the latter imperfectly 

 divided into two cavities by an incomplete septum. The lungs 

 and other paired organs are mostly not bilaterally symmetrical, 

 one of each pair being either rudimentary or absent. There is 

 no urinary bladder, and the cloacal aperture is transverse. 



Of these characters of the Snakes, the most obvious and 

 striking are to be found in the nature of the organs of locomo- 

 tion. The front limbs, with the scapular arch and sternum, 

 are invariably altogether absent; and the hind-limbs, if not 

 wholly wanting, are never represented by more than a pair of 

 rudimentary pelvic bones concealed within the muscles on each 



