484 DR. R. W. SHUFELDT ON [NoV. 16, 



It will at once be seen that Geococcyx calif or nianus, in common 

 with the vast majority of birds, has uo special tendon devoted to the 

 flexing of the second or prebasal phalanx of i\\Q fourth toe (here the 

 reversed one) . Provision is made for this in various ways in different 

 birds. Here, in the subject before us, a special slip is thrown oflp 

 for attachment from the deep flexor tendon as it passes over the 

 prebasal joint in question, which slip virtually fulfils the function 

 of 2i flexor perforatus annularis secundus 'pedis, did such a muscle 

 with an independent tendon exist. 



The flexor perforans digitorum profundus (Plate XLV. fig. 2, 

 fp-p)- This muscle is deep to all the flexors, and is situated directly 

 on the posterior aspect of the tibia and fibula. It arises by two 

 heads, one from the upper part of the tibia immediately below the 

 overhanging rim of its summit, and the other, smaller, from the back 

 of the head of the fibula. In the Corvidse there is a well-developed 

 third head, which comes off' from above the fibular notch of the outer 

 condyle of the femur, and in these birds, too, there is no fibular head 

 to this muscle, but two tibial ones instead. Geococcyx agrees 

 however, with most birds in having this muscle attached nearly the 

 whole length of the posterior aspect of the shaft of the tibia by lightly 

 attached carneous fibres. 



About a centimetre about the tibial cartilage it terminates in a 

 strong subcompressed tendon, which, passing beneath the cartilage 

 referred to, crosses the ankle-joint in front of all the other flexor 

 tendons, and then passes through the inner of the two longitudinal 

 perforations of the hypotarsal apophysis of the tarso-metatarsus. 

 Down the posterior aspect of the shaft; of this bone the tendon still 

 maintains its anterior position and exhibits a predisposition to 

 ossify. But this does not actually take place in the specimen before 

 me. Above the distal trochleae, it makes the fibrous connection 

 with the tendon of the flexor longus hallucis already described. 

 This band is shown in the figure. Once within the limits of the post- 

 trochlear space, the tendon of this muscle behaves in a manner 

 common to most birds — that is, it quadrit'urcates, and each branch 

 takes a course close up to the joints on their plantar aspects, and 

 running through the slits in the perforated tendons pass in each 

 case to the ends of the toes, where they become attached or in- 

 serted upon the infero-proximal tubercles of the unequal phalanges. 

 The one passing along under the fourth digit sends up a slip which 

 is attached to the underside of the shaft of the prebasal joint, thus 

 making good the deficiency here of what is represented in the other 

 toes by an independent tendon. 



The tibial head of this muscle at its origin is directly covered by 

 the soleus, while in the aperture existing between the two heads we 

 can discern the popliteus. 



These flexor muscles, and others on both the front and rear of 

 this limb, are moulded upon each other in a manner that can only be 

 justly appreciated by a personal examination. In some the con- 

 nections are quite feeble, the intervening tissue being easily separable, 

 while in others the intimacy is very close, and great care is 



