10 BRITISH MAMMALS 



composition and articulation with the skull that are essentially 

 mammalian ; by a skull that lacks several of the many separate 

 pieces of bone that goes to its composition in reptiles and 

 birds. But the last of these obvious distinctions (an invariable 

 one) is the manner in which the skull articulates with the first 

 vertebra of the spinal column. This is by means of two 

 separate processes of bone (the condyles), which develop from 

 the end of the occiput, or roof of the skull ; whereas in birds 

 and most reptiles the articulation of the skull with the vertebral 

 column is by means of a single process of bone. There is a 

 double process — two condyles — in the Amphibians (frogs, newts, 

 etc.), but these condyles do not arise from the bones roofing 

 the skull. 



Then, again, the vertebrae of the mammalian neck are 

 markedly different in shape and structure from those of the 

 back, and the neck vertebrae are almost invariably seven in 

 number. There are not a few other and minor peculiarities 

 connected with the bones forming the spinal column, with the 

 ribs, the ankle joint, the ear bones, and the soft parts (that is to 

 say, the muscles and the various organs of the body) ; but as 

 this book is not a scientific treatise, it would be wearisome to 

 go too deeply into these particulars. The main feature in the 

 Mammalia which sharply distinguishes them from other animals 

 is the secretion of milk by which the young are nourished after 

 birth. In all the Mammalia, except the two existing forms of 

 Monotreme in Australia ; ^ the young are born alive. Mammals, 

 therefore, in the eyes of the undiscriminating differ markedly 

 from birds and reptiles, in that they produce their young alive 

 (from eggs so minute that they are scarcely visible to the naked 

 eye). Mammals are not alone in this feature of living-born young. 

 Some fishes and reptiles, extinct and living, have acquired the 



^ The echidna and the duckbill — very ancient and primitive types of 

 mammal vfhich present a good many reptilian features — produce eggs with 

 large yolks, and these eggs are either hatched in the mother's pouch, or 

 perhaps in the case of the duckbill, allowed to hatch separately from the 

 mother, after which the young animal is placed in the pouch. 



