626 MR, P. CHALMERS MITCHELL ON THE [June 16, 
presence or absence of the ambiens muscle as of primary import- 
ance. He divided birds into the Homalogonatz, which possess the 
muscle, and the Anomalogonate, in which it is absent. Here and 
there among groups which certainly must be associated with the 
Homalogonatous birds there are instances in which the ambiens 
is absent, and in which Garrod believed the ambiens to have been 
present, but recently lost. It is of great interest therefore to 
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FLEX. COM. 
Leg-muscles of Opisthocomus cristatus showing vestigial ambiens. 
Glut. 2, Attachment of gluteus medius. Glut. 3, Attachment of gluteus tertius. 
Glut. ant., Gluteus anterior. II. 2. Flexor perforans et perforatus indicis. 
III. 2, Flexor perforans et perforatus medii. Per. 2, Peroneus secundus. 
I. Flexor longus hallucis. II. Flexor perforatus indicis. III. Flexor 
perforatus medii. IV. Flexor perforatus quarti. 
find a species different individuals of which show so great 
variations in the condition of the ambiens muscle, reaching from 
the normal complete condition found by Garrod to the extremely 
vestigial condition in the specimen from which fig. 4 was drawn. 
Some time ago, in a paper communicated to this Society’, I 
recorded the discovery of vestiges of the ambiens in the case of two 
1 “On the Perforated Flexor Muscles in some Birds,” P. Z. 8. 1894, p. 495. 
