1894.] 



MYOLOGY OF RODENTS. 



261 



In the Chinchillidae the muscles are largely attached to the 

 clavicle. 



Iu the Dasyproctidse the scapulo-clavicularis is especially well 

 developed, being considerably larger than the supraspinatus. 



In the Caviidae the small clavicle is between the two muscles in 

 Cavia cobaya, having both attached to it ; but in Ceredon rupestris 

 the subclavius was found to send a few fibres into the clavicle aud 

 a few into the scapulo-clavicularis, but its insertion was chiefly 

 into the anterior border of the acromial process. The scapulo- 

 clavicularis rose chiefly from the clavicle. 



In the Sciuromorpha the subclavius had the usual human attach- 

 ments, but the scapulo-clavicularis was absent in all the animals 

 examined. 



It is interesting to notice that the Dipodidae, so far as this 

 muscle is concerned, differ from all the rest of the Hystrico- 

 morpha. 



The nerve-supply of both parts of this muscle is from a branch 

 from the upper part of the outer cord of the plexus, corresponding 

 to the human nerve to the subclavius. 



Kg. 2. 



Shoulder-muscles of Ceredon rupestris. 



1. 



Deltoid (clavicular). 



5. 



Trapezius (cut). 



2. 



„ (acromial). 



6. 



Subclavius. 



si 



„ (spinous). 



7. 



Clavicle. 



4. 



Levator clav. (cut). 



8. 



Acromion and mctacromion. 



Deltoid. — The deltoid in Rodents consists of three parts, which 

 are liable to become more or less fused with one another. The 

 first part rises from the outer part of the clavicle, the second from 

 the acromial and metacromial processes, while the third part 



Pboc. Zool. Soc— 1894, JS T o. XVIII. 18 



