156 MB. fl. a. SEELET ON OSSEOUS EESEMBLAWOES 



and small malar of the Ant-eater, essentially reproduce what 

 obtains in the Crocodile, though the arch is entire in Crocodiles 

 and the malar is not styloid : the nasal bones also conform to the 

 Crocodilian type, and the premaxillary bones are relatively as 

 small. From the absence of a transverse bone in mammals, there 

 are no palatal pterygoid fossae as in the Crocodile. But for the 

 dicondyloid articulation, the back of the Ant-eater's skull is in 

 many respects Avian. 



The next nearest resemblance among maminals to the palate 

 of the Crocodile is seen in the Cetacea, where the teeth are in 

 some respects similar ; yet the Crocodile is peculiar in having 

 the posterior nares entirely embraced by the pterygoid bones. 

 And the Porpoises diverge far from Crocodiles in the backward 

 position of the anterior nares, by which the premaxillary bones, 

 owing to their relation with the extremity of the snout and the 

 nares, come to be developed to a great length. The scarcely 

 divided occipital condyle is made by the exoccipital bones in 

 Dolphins, and not chiefly by the basioccipital bone as in Croco- 

 diles. 



Perhaps the nearest resemblance among mammals to the ex- 

 ternal form of frontal bone of the Crocodile, is seen among 

 Eodents like the Eabbit, in which the orbits are relatively large 

 and approximate closely. But in Crocodiles the bone does not 

 close in the brain, and is undivided laterally, which is rarely the 

 case with mammals. 



In the vertebral column Crocodiles have but little in common 

 with mammals and are distinguished from them by many charac- 

 ters. Their vertebrae are procoelian ; they have cervical ribs. Their 

 dorsal ribs are attached by double heads to long transverse pro- 

 cesses ; only one or two of the vertebrae between the neck and 

 back have the lower head of the rib attached to the centrum. 

 This condition is characteristic of the dorsal vertebrae in Myrme- 

 cophaga, while in the majority of mammals the rib articulates 

 with two vertebrae. And it is only among Cetacea, especially the 

 true Whales, that the dorsal ribs are supported on long trans- 

 verse processes as among Crocodiles. But the ribs of true 

 "Whales differ alike from those of mammals, birds, and Crocodiles 

 in having but one head for the rib as among Lizards &c. The 

 caudal vertebrae retain the neural arch to the end of the tail, 

 which is not the case with mammals. Some of the chevron 

 bones have the two articular facets connected by a transverse 



