1896.] MIOLOGY OF nODBNTS. 167 



/? vises from the whole length o£ the sternum ; y (the abdominal 

 fibres) are feebly marked ; I (the part corresponding to the pec- 

 toralis minor) comes from the lower true rib-cartilages and runs 

 forward and outward to the head of the humerus and to the cora- 

 eoid process. Heteromys only differs from this description in 

 having the abdominal fibres more closely united with the panni- 

 culus than in any other animal. In the Gerbille, o aud /3 are fused, 

 while y and Z unite near their insertion, which is into the capsule of 

 the shoulder and into the humerus just internal to the pectoral ridge. 

 Tlie Hamster differs from the last only in having the abdominal 

 fibres better developed and running quite separately to the cora- 

 coid process. The Vole closely resembles the Gerbille, but is 

 remarkable for the great development of the fibres from the 

 cartilages (S) ; these fibres unite with y, and are inserted into the 

 coracoid. 



In the Rat and Mouse the arrangement is almost identical with 

 that of the Gerbille. 



In Sijihneus Milne-Edwards describes a large and distinct pec- 

 toralis minor inserted into the coracoid process and coming from 

 the second rib ; this is interesting when one notices the similar 

 arrangement in the Vole, an animal to which he regards Siiyhneus 

 as being more closely related than to the Mole-Rats '. 



lihizomys resembles Cricetomys except that 5 is larger, rises from 

 the 2nd to the 7th costal cartilages, and is inserted into the clavicle 

 as well as the liead of the humerus. Georychus has a and /3 fused ; 

 y is inserted into the neck of the humerus ; 2 rises from the 2i]d, 

 3rd, and 4th costal cartilages and is inserted into the coracoid and 

 shoulder-joint. 



In Bathyergits the pectoral mass is very large, and resembles the 

 last in having a and /3 fused ; but near the insertion the posterior 

 fibres become tucked under the anterior and are inserted deep to 

 them into the pectoral ridge. The abdominal fibres (y) rise from 

 the end of the sternum to the middle of the linea alba ; they are 

 inserted together with a large part of the latissimus dorsi into the 

 capsule of the shoulder. The pectoralis minor (5) rises from the 

 posterior two-thirds of the sternum and the posterior true rib- 

 cartilages, and is inserted into the outer half of the clavicle, having 

 its anterior boi'der in contact with the posterior border of the 

 subclavius ; between these two contiguous borders the external 

 anterior thoracic nerve emerges to reach the superficial parts of 

 the muscle. 



Sterno-scapularis. — In the greater number of the Myomorpha 

 this muscle is only represented, as in Man, by the subclavius, which 

 rises from the cartilage of the first rib and is inserted into the 

 outer half of the posterior border of the clavicle. Georyclms and 

 Balhyergus are the only exceptions which I have met with ; in these 

 there is a large and distinct claviculo-scapularis, as in the Hystrico- 

 morpha. In Siphneus, according to Milne-Edwards, the arrange- 

 ment is the same. 



' ' Eecherches dea Mammiferes,' tome i. p. 99. 



