STUDIES OF THE MACROCHIRES. 



357 



eliest-rnuscles as they occur in the group. In every individual 

 instance I found the state of affairs essentially the same, and 

 the Swallows agree with all true Passerine birds which I have 

 thus far examined, in possessing all throe of the pectoral mus- 

 cles. The pectoralis tertius is, comparatively speaking, very 

 large, and arises nearly or quite as far back on the anterior aspect 

 of the sternum as the pectoralis seci/ndus does ; it also arises, as 

 is usual, from the outer side of the shaft of the coracoid bone of 

 the shoulder-girdle. Pectoralis major makes a very broad and 

 strong tendinous insertion at the ordinary site upon the shaft of 

 the humerus, while the tendon of the second pectoral passes 

 through the usual canal formed by the juxtaposition of the bones 

 of the shoulder-girdle. Tn texture the fibres of the great pectoral 

 in Swallows seem to be always coarse and of considerable size. 



To these characteristics with respect to the pectoral muscles 

 as I found them in the smaller representatives of the group, 

 Progne suhis forms no exception. 



Of the Muscles of the Thigh. 



According to Garrod all Passerine birds exhibit, for the classi- 

 ficatory group of muscles of the thigh, the myological formula 

 A. X. Y (except Dicrurus, wherein it is A. X) ; i. e., they possess 

 the femoro-caudal, the semitendinosus, and the accessory semi- 

 tendinosus — the accessory femoro-caudal and ambiens being 

 absent. Upon carefully examining the Swallows, I find that this 

 is also the rttle with them ; and these muscles seem to be about 

 equally well developed in the several genera, although it struck 

 me that the accessory semitendinosus was, comparatively speak- 

 ing, rather feebly developed in Frogne. Beyond these special 

 muscles, I did not investigate the myology of the pelvic limb of 

 these birds. 



Notes on the Arterial System. 



Swallows, in common with other Passeres, also have but one 

 carotid artery, the left, which cotirses up the neck, as usual, in 

 the hypapophysial channel at the mid-anterior aspect of the cer- 

 vical vertebrae. And in the pelvic limb the main artery I found 

 to be the sciatic, which is likewise the rule among the Passerine 

 birds, and Professor Garrod found but few exceptions to this. 



