34 ME. W. P. PTCEAFT ON THE 



lower fifth or sixth of the inner side of the distal end of the shaft. The fibula in Ketupa, 

 and less distinctly in Bubo, Nyctala, and Strix, may be traced downwards as far as 

 the proximal tarsal mass. In Syeotyto it fuses indistinguishahly with the tibial shaft 

 rather below the middle of it ; in Scops it reaches as far as the distal sixth of the shaft ; 

 in Carine it extends some distance beyond the middle of the shaft, but not so far as in 

 Scops. The fibular ridge borne by the tibia is fairly strongly developed, but varies 

 slightly in length. It is short and near the proximal end of the shaft in Megascops, 

 Nyctala, and Carine, long and low in Asio, Bubo, Ketupa, and the Strigidse ; for example, 

 Scops and Speotyto have this ridge only feebly developed. 



The tarso-metatarstis is remarkably Falconiform in its general conformation ; it may be 

 distinguished, however, by the presence of an extensor bridge — which is rarely absent — 

 and the disposition of the trochleas. 



The length of the shaft varies much, being in some shorter than the femur, e. g. 

 Scops, Nyctala, Carine ; and in others longer than the femur, e. g. Speotyto, Strix. In 

 Bubo, Ketupa, and Oymnoscops these two segments are subequal. 



The hypotarsus is simple, being formed by a prominent and more or less quadrate 

 bony plate arising from the inner border of the proximal end of the shaft. A deep 

 groove divides this from a much smaller, laterally compressed plate arising from the 

 outer border of the shaft somewhat higher up, so that its superior border contributes 

 towards the formation of the glenoid surface for the ectocoudyle of the tibio-tarsus. Not 

 seldom the inner calcaneal process takes part in the formation of the glenoid surface for 

 the entocondyle of the tibio-tarsus. 



The shaft is grooved both on its anterior and posterior surfaces. Anteriorly the 

 groove is confined to the proximal end of the shaft, and is both wide and deep. This 

 feature is especially noticeable in the larger species of Bubo. In these the groove takes 

 the form of a deep and wide fossa lying at the proximal end of the inner border of the 

 shaft, and is crossed by an extensor bridge. 



Mesially this fossa is bounded by a flat wall forming one side of a triangle, the other 

 side forming the outer border of the shaft. Within this fossa lies a long narrow scar, 

 the impression for the tibialis anticus. The posterior surface of the shaft is deeply grooved 

 throughout, and 2oerforated just below the hypotarsus by a small oblong foramen. Seen 

 in section the shaft, below the hypotarsus, is eo-shaped, but lower down o-shaped. In 

 Ketupa and the smaller Owls, the anterior groove extends across the whole face of the 

 shaft. The posterior groove agrees with that of Bihbo just described. 



The trochleas differ from those of the Palconiformes in that they are disposed in a 

 more strongly curved arch, and in that the third trochlea is much shorter than the first 

 and second — which are on the same level one with another — and directed backwards. 

 There is, it may be remarked, a passing resemblance in the form and disposition of the 

 trochleas between the Striges, and especially Ketupa and Pandion among the Accipitres ; 

 but whereas in Pandion the 2nd trochlea has its mesial border strongly raised above the 

 level of the shaft, and sloping inwards to over-arch trochlea 1, in Ketupa the middle 

 trochlea presents no strongly developed ridges and is widely separated from trochlea 1. 



