i895. MUSCLES AND CLASSIFICATION. 339 



stress is the " supinator longus," a muscle that tends to disappear on 

 very shght provocation. It is present in all the Sciuromorpha that I 

 have examined, with the exception of the beaver ; that is to say, it is 

 present in the squirrel, the flying squirrel {Ptevomys), the ground 

 squirrel {Xevus), the marmot, and the gopher. I am unable to say 

 whether it is found in the families of the Anomalures and Haplodonts 

 as I have never had an opportunity of dissecting examples of these, 

 and can find no records of such dissections; but there is no doubt that 

 the muscle is a very common one among the generalised squirrel sub- 

 order. In the Myomorpha it is not found at all. Among the 

 Hystricomprpha I have never seen it, but I find an account of it in 

 tree-porcupines, dissected by Mivart ' and Windle.^ In the Lago- 

 morpha it is also absent. It may be said that this is a muscle which 

 depends very much on the climbing habits of its possessor, and in a 

 certain sense this is true ; but the point on which I wish to lay stress 

 is that the marmot, which does not cHmb and is a near relative of the 

 squirrel, has a well-developed supinator, while the tree-porcupine, 

 Sphiiigitvns, has no trace of it — indeed, in Windle's specimen of 

 Erethison it was quite rudimentary. If further evidence be needed 

 that its presence does not necessarily imply climbing, one may point 

 to the fact that it is present in the jerboas, three different species of 

 which I have examined. 



The supinator longus is also valuable in the Carnivora, for it is 

 present in the Felida^, Procyonidse, and Ursidse, but absent in the 

 Hyaenidae and Canidae. It is more important, however, to notice its 

 distribution in the rodents ; since some authors, even in books of 

 reference, have stated that it is absent in this Order. 



It is not only the presence or absence of certain muscles that 

 varies with the classificatory position of animals ; the attachments 

 are also valuable. A good instance of this is the " levator claviculas" 

 or acromio-trachehen ; in the Sciuromorpha and Myomorpha this 

 always rises from the atlas, while in the Hystricomorpha it is most 

 inconstant, in some cases rising from the atlas, and in others from the 

 basioccipital. It will be a" good test to pick out those animals in 

 which this change of origin has been effected, and to see whether 

 there is any marked similarity in their mode of life which might 

 account for it. The animals in which I have found the basioccipital 

 origin are the African ground rat [Aulacodns) which inhabits cane- 

 brakes, the hutia [Capromys) an arboreal form, the coypu [Myopotamns) 

 which is aquatic; the ground-porcupines {Hystrix and Atheniva), and 

 the spotted cavy {Coelogenys) which are terrestrial forms, as well as 

 three genera of the family of Caviidae [Cavia, Ceredon, and Dolichotis), 

 all of which are also terrestrial. This list, I think, does not point to 

 the change of attachment being due to any definite change in the 

 animals' mode of life. Hitherto I have only instanced muscles which 

 indicate the sub-order to which the animal belongs ; but it would be 



1 Proc. Zool. Soc, 1S82, p. 271. -^ Journ. Anat., xxii., p. 126. 



