STUDIES OE THE MACROCHIRES. 
357 
chest-muscles 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 three 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 secunclus 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. In 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 subis 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. T (except Dicrurus, wherein it is A. X) ; i. e., they possess 
the femoro-caudal, the semitendinosus, and the accessorj r semi- 
tendinosus — the accessory femoro-caudal and ambiens being 
absent. Upon carefully examining the Swallows, I find that this 
is also the rule 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 Progne. 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 courses 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. 
