292 SHOULDER-GIRDLE IN MONOTREMES, 



brevis ; and its insertion lies between the sterno-epicoracoid inter- 

 nally and epicoraco-brachial externally. 



Origin, (b) M. sterno-epicoracoideus. — This muscle springs 

 from a small portion of the inner (sternal) end of the dorsal 

 surface of the first rib ; from the outer border of the dorsal surface 

 of the presternum ; and slightly from the posterior part of the 

 dorsal surface of the interclavicle. (Fig. 4, A. St. C). 



Insertion. Running forward the muscle is inserted on the 

 anterior half of the dorsal surface of the epicoracoid. 



Relations. This muscle is closely related at its origin to 

 the inner fibres of the costo-coracoid. At its insertion it lies 

 dorsal and internal to part of the epicoraco-brachial. 



Ornithorhynchus. 



Origin, {a) M. costo-coracoideus. — This muscle arises from 

 the inner (sternal) two-thirds of the anterior border of the first 

 rib. (Figs. 7 et 5, Cc). 



Insertion. The origin is fleshy and the muscle fan-shaped, 

 the fibres converging as the muscle runs forward to be inserted 

 on the whole of the dorsal rim of the coracoid adjoining the 

 coraco-presternal arthrodia. The inner fibres of the muscle can 

 with little difiiculty be separated from the main mass, and they 

 are seen to be inserted on the inner portion of the rim above- 

 mentioned, and also by a tendon on the postero-external portion 

 of the epicoracoid. The direction of the fibres of this muscle is 

 not the same as that of the external intercostals, whose fibres run 

 forwards and outwards. 



Relations. At its origin the muscle reaches externally to 

 the origin of the serratus from the first rib. The muscle lies, as 

 in Bchidiia, dorsal to the epicoraco-brachial, and its internal 

 border is somewhat covered by the M. sterno-epicoracoideus. 



Origin. (b) M. sterno-e2ncoracoidetis springs from a small 

 area on the dorsal surface of the first rib, close to its articulation 

 with the presternum ; from the prominent ridge on the dorsal 

 surface of the presternum (this ridge forming the rim of the coraco- 

 presternal arthrodia). 



