252 MB. F. G. PAESONS ON THE [Mar. 20, 



Cavia cobaya. ; Pteromys oral. 



Ceredon rupestris. 

 Dipus cegyptius. 

 Dipus hirtipes. 

 Alectar/a indicci. 

 Sciurus prevosti. 



Xerus getulus. 

 Spenno2>Mlus mexicanus. 

 Arctomys marmotta. 

 Castor canadensis. 



Full use has been made of the accounts of the myology of 

 Capromys fournien by Owen, of Capromys melanurus by Dobson, 

 of Erethizon dorsatus by Mivart, and of Erethizon epixanthus by 

 Windle. I have been also much indebted to the thorough account 

 of the myology of the Crested Agouti by Mivart and Murie, to 

 the writings of Bobson, and to the French translation of Meckel, 

 as well as to worlc done by other authors. 



In this manner six families of the Hystricomorpha have each 

 been illustrated by types of two or more orders, and although 

 more material would no doubt have added to the accuracy of the 

 generalizations, it is hoped that a step has been taken in the road 

 commenced by Mivart and Murie nearly thirty years ago. In 

 tlie Sciuromorpha the supply of material has not been so plentiful, 

 but this is less to be regretted because these animals do not seem 

 to differ so much in their myology as the Hystricomorpha. 



The Dipodidse have been included among the Hystricomorpha, 

 although, as will be pointed out in the general summary, they 

 differ from the rest of the group in certain important particulars. 

 Want of space has prevented the exact attachments of the muscles 

 being chronicled in each animal, and I have contented myself with 

 generalizations wherever possible. 



Occasionally from various causes the whole of the muscles of 

 some of the animals were not available for dissection or were 

 overlooked ; I have therefore, whenever it seemed neiessary, placed 

 in brackets the names of the animals on which the generalizations 

 are founded. 



Muscles of the Head and Neck. 



Temporal. — The temporal muscle is always small, and rises from 

 the side of the head above the external auditory meatus, the two 

 muscles usually coming into contact in the middle line. It also 

 derives some fibres from the inner side of the zygoma. The por- 

 tion coming from the side of the head changes its course when it 

 reaches the posterior root of the zygoma, which it uses as a pulley. 

 The whole muscle is inserted into both surfaces and the anterior 

 border of the coronoid process and part of the bone below. M. 

 J. Kunstler, in his article " Uappareil masticateur des Eongeurs," ' 

 describes the temporal of Arctomys as consisting of three parts — 

 a superior from the parietal bone, a middle from the temporal, and 



' Annales des Sciences naturelles, ser. 7, t. iv. p. 150. 



