54 ANATOMY OF THE DOMESTIC FOWL 



inner proximal surface of the metatarsus. This has been called 

 by Gadow a sesamoid bone. 



The shaft shows tendonal grooves which are best marked on the 

 posterior surface. The shaft is rounded at the sides and flattened 

 on the anterior and posterior surfaces. At the juncture of the 

 middle and inferior thirds of the metatarsus there is a conical process 

 turned slightly backward, which serves as a base for the spur. The 

 spur is a horny structure. 



At the distal extremity occurs the threefold trochlear arrangement 

 mentioned above, which incloses the fossa intercondyloidea. The 

 inner trochlea is the broadest, and the outer the narrowest. The 

 inner trochlea articulates with the proximal end of the second, the 

 middle with the third, and the outer with the fourth toe. 



The Phalanges. Location. Most domestic fowls are provided 

 with four digits, or toes; the Houdan and Dorking are provided with 

 five. In fowls with four toes the three principal toes, the second, the 

 third, and the fourth, are directed forward, and the first, or hallux, 

 is directed backward. 



Description. The last phalanx of each toe, called the ungual 

 phalanx, is slightly curved downward, is pointed anteriorly, like 

 the claw of the cat or dog, and -is covered with a horny sheath. The 

 articular ends of the joints of the phalanges are enlarged. Tbe base 

 of the basal phalanx has two enlargements, the superior-inferior 

 tubercles, or tuberculum superius et inferius, between which is lo- 

 cated the fossa articularis transversa. Laterally the head has two 

 condyles, condyli laterales, which are divided by the sulcus longi- 

 tudinalis. The bodies of the phalanges vary in form; they are supe- 

 riorly rounded, but inferiorly rounded, flat, or even somewhat con- 

 cave. The distal extremity has an articular trochlea. 



The first toe, or digit, called the great toe, or hallux, is composed 

 of three phalanges, or segments. The first segment, or basal 

 phalanx is considered a rudimentary metacarpal bone; it is at- 

 tached by a fibrous cartilaginous tissue to the inner posterior 

 surface of the inferior extremity of the metacarpal bone just be- 

 low the spur. 



The second toe, likewise composed of three phalanges, is directed 

 forward. It articulates with the inner trochlea located on the 

 inferior metacarpal bone. 



The third toe, made up 'of four phalanges, is the middle of the 



