MUSCULAR SYSTEM OF AVES. 109 



ends in a strong flat tendon at the lower third of the leg, which 

 tendon runs through a particular sheath at the back part of the 

 tarsal pulley, becomes thickened and expanded as it advances 

 forwards beneath the tarsus, joins the tendon of the flexor perfo- 

 ratus, and forms with it the expansion which finally divides into 

 three strong perforating tendons, which bend the last joints of the 

 three long toes. 



In the outer, or fourth toe, both the perforans and perforatus 

 tendons are confined by a double annular ligament ; the exterior 

 one being continued from the adjoining toe, the inner and stronger 

 one from the sides of the proximal phalanx of the outer toe. The 

 second and third toes have two perforated tendons ; one inserted 

 into the sides of the first, and the other into the sides of the second 

 phalanx. 



The chief modification of the skeleton of the hind limb of Birds, 

 in respect of size and proportion, is manifested in its central 

 segment ; the ossa innominata being anomalously expanded in 

 order to include, as it were, in their grasp the whole of the very 

 long sacrum required for the support of the horizontal trunk 

 upon a single pair of extremities. The principal modification of 

 the muscles of the leo' attached to the ossa innominata mijiht 

 be expected, therefore, to be found in their origins. In the at- 

 tachment of the fibres of a superficial muscle to the aponeurosis, 

 continued from the outer part of the thigh, over the knee-joint, to 

 the head of the tibia, we recognise the corresponding insertion of 

 the tensor vagincB femoris of Man and Mammals ; and no Com- 

 parative Anatomist appears to have thought the anomalous de- 

 velopement and extensive origin of this muscle, in Birds, to be 

 any objection to the homology indicated by its insertion, which is 

 the attachment that mainly governs the function of a muscle, 

 Now besides the attachment to the femoral fascia, we find this 

 broad superficial muscle, and especially its middle and posterior 

 fibres, terminating in a strong tendon, implanted into the upper 

 part of the patella, and receiving fibres from the crurceus and vasti 

 muscles which it immediately covers, and with which it concurs in 

 constituting a quadriceps extensor of the leg. Here, therefore, 

 we perceive the normal insertion, the normal function, and the 

 true relative position of the rectus femoris. In calling this 

 complex muscle ' abductor mognus^ it is to be understood as 

 including the homologues of the tensor vagince femoris and rectus 

 feinoris in Mammals. 



§ 135. Muscles of the Skin. — In the Apteryx the cutaneous 

 system of muscles presents a distinct and extensive developement 



