116 BULLETIN UNITED STATES GEOLOGICAL SUEVEY. [Tol.Yl. 



at its distal extremity, for examination, the trochlese tliat articulate with 

 the rear segment of all the toes except hallux. Viewing this end with 

 the bases of these trochlese towards one, we find the general outline 

 made by them to be truly crescentic, with the horns having a tendency 

 to approach each other behind. The outer trochlea is the highest and 

 longest from before backwards ; the other two are about on the same 

 level, the inner one having a posterior and internal process, while the 

 middle one is possessed of a median cleft traversing its face antero- 

 posterioiiy. They are sharply divided from each other by narrow slits, 

 that extend up as far as the articulating part, and are continued on the 

 anterior aspect of the shaft for a short way as delicate groovelets. A 

 foramen is situated in the outer of these, that gives passage to the an- 

 terior tibial artery, and is comparatively larger than usually seen in the 

 Owls. Behind, the tendinal groove expands, and is bounded distally by 

 the concave border formed by the trochlese. Upon its internal margin, 

 just above the extremity of the bone, it shows an elongated but feebly 

 marked depression of about 3 millimetres in length. This facet articu- 

 lates with the OS metatarsale accessorium, which is joined to the bone 

 by ligament. This little bone in this bird has an average length of 4 

 millimetres. It is twisted upon itself, and bears upon one border a con- 

 vex, smooth surface for the tarso-metatarsus, while distally it has an 

 articulating surface, resembling more the mid-trochlea than any other, 

 for the proximal segment of the hallux. Above it is sharply grooved 

 for the tendon that goes to that toe. The toes are four in number, and 

 their bony segments follow the rule that governs the greater part of the 

 class Aves ; that is, first, second, third, and fourth toes have 2, 3, 4, and 

 5 phalanges allotted to them, respectively. The first phalanx of the 

 hind toe is more compressed from side to side than in the other toes, 

 possessing more of the characteristics of the second joints. Its posterior 

 facet, that articulates with the accessory metatarsal, fits accurately into 

 the cleft surface seen on that little bone. Anteriorly the facet has a 

 median groove, forming two vertical convexities for the double concave 

 facet on the claw, with its dividing ridge. The claws are all a good deal 

 alike, varying in size, the rear one being the most compressed laterally. 

 They are pointed, arched, and nearly conical, the horny thecse that cover 

 them during life only being grooved on the under side. Their proximal 

 ends have an articulating facet for the next phalanx behind them ; this 

 is so arranged that they can be more smartly flexed than any of the 

 other joints of the foot, due to the convex articulating surface extending 

 well beneath on the phalanx they meet. On the under sides of their 

 proximal extremities is a tuberosity for the attachment of the flexor 

 tendons ; it has on either side, below, an oval foramen to aUow vessels 

 and a nervelet to pass to the extremities of these ungual phalanges. The 

 first joint of the second toe, and the first and second of the third, are 

 thickset and short, articulating internally with the tarso-metatarsus, and 

 having their facets so arranged as to allow of motion only in the one 



