ADAPTATIONS 119 



rows ; while the transverse rows severally correspond with one 

 segment of the skeleton of the trunk. In most species there is 

 a detached patch of plates on the neck ; and the larger scales 

 on the back, like those of the neck-patch, are longitudinally 

 keeled. As the tail is approached, the middle series of plates 

 is gradually squeezed out, while the lateral ones approximate, 

 till they finally meet in the middle line, where they lose their 

 bony plates, with a proportionately greater development of the 

 horny covering. In gharials {Garialis and Tomistojiia), true 

 crocodiles {Crocodilus), and true alligators {Alligator) the 

 dermal armour is restricted to the upper surface, but in the 

 African crocodile representing the genus Osteolcemus a few 

 bony plates are developed in the throat, and in the caimans, or 

 South American alligators {Caiman), a buckler of thin bony 

 plates is developed on the abdominal surface. This ventral 

 buckler comprises more than eight longitudinal rows of plates, 

 each plate composed of two separate pieces of bone, con- 

 nected with one another by suture. The degree of develop- 

 ment of this armour varies in the different species, the culmination 

 occurring in the high-crowned caiman {Caiman palpebrosus). 

 In that species not only does the ventral armour cover 

 the greater part of the lower aspect, but the limbs are invested 

 in complete bony sheaths, which cover even the toes like 

 gloves. The patch of plates on the nape of the neck is 

 also connected with the armour of the back. Such a 

 complete bony panoply appears to be met with elsewhere 

 among living reptiles only in Testudo emys and a nearly 

 related species. Why this particular species of caiman should 

 require such a complex armour has not yet been ascertained. 



In the crocodiles of the Jurassic epoch the armour differs 

 considerably from that of existing types. In the family Gonio- 

 pliolididte, for example, the dorsal plates are rectangular and 

 may be arranged in two or in several longitudinal rows ; while 

 the ventral armour may form either a single or a double 

 buckler, in which the posterior transverse rows of plates may 

 overlap like the tiles on a roof, or may be articulated together 

 by suture, each plate consisting of only a single element. In 

 the typical Goniopholis, as represented by the " Swanage croco- 

 dile " of the Dorsetshire Purbeck, the plates of the dorsal 

 buckler present the peculiarity of articulating with one another 



