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Show 252 MR. P. G. PARSONS ON THE [Mar. 20, Cavia cobaya. Pteromys oral. Ceredon rupestris. Dipus ceguptius. Dipus hirtipes. Alectaga indica. Sciurus prevosti. Xerus getulus. Spermophilus mexicanus. Arctomys marmotta. Castor canadensis. Full use has been made of the accounts of the myology of Capromys fournieri 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 Dobson, and to the French translation of Meckel, as well as to work 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 the 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, aud 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 necessary, 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 portion coming from the side of the head changes its course when it reaches the poster;or 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 " L'appareil masticateur des Bongeurs," ' describes the temporal of Arctomys as consisting of three parts- a superior from the parietal bone, a middle from the temporal, and 1 Annales des Sciences naturelles, ser. 7, t. iv. p. 150. |