THE MUSCLES OF THE UPPER EXTREMITY. 71 



and wide in the Natatores generally, but in the Penguin, 

 its origin is limited to the external margin of the 

 subjacent pectoral muscle, which is here remarkably 

 developed. The great pectoral is very long, but not 

 very thick in the Easores. In the Herons it is shorter, 

 but much stronger and thicker. Its size is most 

 remarkable in the Humming-birds, Swallows, and 



Fig. 25. — Anterior aspect of Ihe sterr.uni of a Raven, designed to sliow the areas 

 of origin of the pectoral group of muscles. The subclavius lies beneath 

 the p. tertvus. Life-size, from the specimen. 



diurnal birds of j)rGy, where it is attached to almost the 

 whole outer surface of the sternum, and its crest, 

 and has an extended insertion. In the Ostrich its 

 origin is limited to the anterior and external eighth 

 part of the sternum, and it is inserted by a feeble 

 tendon into the commencement of the pectoral 

 crest of the humerus, to which it gives a strong rotary 

 motion forwards. In the Apteryx the pectoralis major 



