344 



THE AMERICAN MUSEUM JOURNAL 



Attention may be called to the relatively enormous size of the skull and the 

 curious way in which the long point of the lower jaw passes up into the groove 

 in the upper. 



We find many other mammal-like reptiles of which the Therocephalians, 

 Dromasaurians, and the Cynodonts are the most important. Although 

 these insectivorous and carnivorous types are less mammal-like in some 

 respects than the Anomodonts, they agree more closely with the mammals 

 in the construction of the skull. They all have long, slender limbs adapted 

 for running. The earlier members such as the lower Therocephalians, have 

 the number of toe joints as still found in the lizards and most reptiles, viz. — 

 2, 3, 4, 5, 3 ; but the Anomodonts, the lower Dromasaurians and the higher 

 Cynodonts have the same number of joints in the toes as is retained in our- 

 selves viz. — 2, 3, 3, 3, 3. It is rather interesting to look at one's hand and 



Inostrancevia alexandri Amalitsky. A photograph of a skeleton of one of the large mam- 

 mal-like reptiles found fossil on the banks of the Dvina River in north Russia. The skeleton 

 is of large size, the skull being about two feet in length and is extremely closely allied and 

 perhaps identical with some forms found in South Africa 



realize that the fingers have all these joints because a remote ancestor took 

 to walking with the feet under the body supporting it off the ground rather 

 than with the feet to the side as in the lizards and crocodiles. 



The Cynodonts occur in the Triassic formation and a few survive into the 

 Jurassic. In most points of structure they are extremely mammal-like and 

 it is frequently impossible if the specimen is at all incomplete to say whether 

 we are dealing with one of the Cynodonts or a mammal. The lower jaw is 

 almost entirely formed by a large single bone, the posterior bones being 

 small, and the bone on which the jaw hinges is also small thus foreshadowing 

 the mammalian condition, the dentary bone, the angular, articular and sur- 

 angular being quite small, as is also the quadrate bone. The teeth are in 

 most forms of a carnivorous type, composed of sharp incisors, long sharp 



