.4D.l.l/,s', PHYLOOENY OF THE JAW MUSCLES 53 



US one of the best types of comparative work at present available. Toldt, 

 Bijvoet, Chaine, Eouviere, Parsons, Dobson and others have traced the 

 digastric muscle in the mammals, giving homologies and tracing the 

 muscle to its origin in the lower forms. The many writers on the muscles 

 of special groups have used synonymous names and the nomenclature is 

 far from clear at the present time. Many names for muscles are used 

 in special cases that might w^ell be changed to give a more uniform system. 

 The influence of the musclature upon the evolution of the skeleton in 

 vertebrates has also been neglected in most of the general works on com- 

 parative anatomy. Much has been written on the changes that have 

 taken place in the skulls of the vertebrates, but with too little reference 

 to the muscles. The palaeontologists and anatomists have traced the 

 shiftings and changes of each bone in the skull so that the migrations of 

 the hyomandibular and of the quadrate, for example, are known from the 

 time when they appear as cartilages in the selachians to their final resting 

 place in the mammalian ear. Thus during the last decade or two oste- 

 ology has made great progress as an interpretative science. From the 

 work done on the fossil forms the evolutionary history of the skeleton is 

 not nearly so obscure as it was a few decades ago. The structure of many 

 of the fossil forms is being gradually worked out and some of the great 

 vertebrate phylogenies are being cleared up by the recent developments 

 in palaeontology and comparative anatomy. For example, the relatively 

 close relationship between the reptiles and the amphibians is becoming 

 very clear, for the discovery of new Carboniferous forms has added much 

 to our knowledge, so that more and more structures common to the two 

 classes have been observed. The same applies to the relationship of rep- 

 tiles and mammals. The recent discoveries in South Africa of a number 

 of new cynodont reptiles have given much new light on the evolution 

 of the mammals from the reptilian stock, so that great advances have 

 been made in the early history of these relatively modern groups. Manv 

 morphological problems, such as the problem of the mammalian pterygoid 

 and its origin, of the ossicles of the ear, of the development of a new 

 joint on the dentary, and its new articulation with the squamosal, have 

 received illumination from the synthesis of palcieontolog}^ and com[)arative 

 anatomy. In all such studies the great working tool of the palaeontologist 

 is comparative anatomy, as without it he is helpless to determine tlie 

 relationships of the fossil forms, just as the student of modem forms is 

 hel]iless if he attempts to work out the relationships of the modern fauna 

 without considering the maze of ancestral types that preceded them in 

 the past. Thus the importance of tlie modern forms is demonstrated 

 every day in the great nniseums of palaeontology arid comparative anatom}' 



