ORDER CROCODTLIA. 1 1 85 



yields the remains of Phytosaurus, and is very imperfectly known. 

 It differs from the preceding family by the structure of the ventral 

 part of the basioccipital, which approximates to the Rhynchoceph- 

 alian type. 



Suborder 3. Eusuchia. — This suborder is taken to comprise 

 all the post-Triassic Crocodilia. These were, indeed, originally 

 divided into two suborders, but subsequent researches have shown 

 that they are so closely connected as to render such division inad- 

 visable. In all these forms the premaxillae, maxillae, and palatines 

 develop inferior palatal plates meeting in the middle line beneath 

 the narial passage, and thus completely separating the latter from 

 the mouth, and causing the formation of secondary posterior nares, 

 which in some instances are situated immediately behind the pala- 

 tines, but in others (as in the figure of Crocodilus given on page 

 1 192), owing to the development of similar plates by the pterygoids, 

 behind the latter bones. The object of this peculiar arrangement 

 is to enable these animals to drown their prey by holding it in their 

 open mouths under water, which is thus entirely prevented from 

 entering the air passages. A gradual evolution of this structural 

 feature can be traced from the last suborder, where it is entirely 

 wanting, to the generalised, and thence to the most specialised, 

 members of this division. Other characteristic features are found 

 in the terminally -situated, and usually undivided, nares ; in the 

 non-appearance of the vomers on the palate ; in the bony middle 

 eustachian canal ; and the presence of not more than four or 

 five teeth in the premaxillae. There is no clavicle; the coracoid 

 is much elongated ; the pubis is entirely excluded from the ace- 

 tabulum (fig. 1 081) ; and there are five digits in the manus and four 

 in the pes (fig. 1079). This suborder may be divided into two 

 series according to the development or non-development of palatal 

 plates by the pterygoids, and the form of the vertebrae. 



The occurrence in all the groups of the Eusuchia of long-jawed and 

 short-jawed forms is so suggestive of the direct origin of the existing 

 Gharials from long-jawed Mesozoic types, and of the Crocodiles. and Alli- 

 gators from short-jawed forms of the same epoch, that Dr Koken adopts 

 this view, and divides the families according to this grouping. There is, 

 however, considerable difficulty in accepting this view, since it would 

 appear unlikely that all the modern Crocodilians would have attained 

 such a similarity in cranial and vertebral characters if they had totally 

 different origins. 



A. Amphiccelian Series. — In this the more generalised series 

 the centra of the vertebrae are usually amphiccelous ; the pterygoids 

 do not develop palatal plates ; and the dorsal scutes are usually 

 arranged in only two longitudinal rows, and are keel-less. The 

 ventral buckler is generally divided into an anterior and a posterior 



