30 ME. W. P. PYCEAFT ON THE 



VII. The Pelvic Girdle. 



The pelvic girdle of the Striges bears a very close resemblance to that of the Accipitres, 

 among the Falconiformes. As in the Accipitres, the innominate bones are never free in 

 the adult, the preacetabular ilium is very long, and the pectineal process is wanting. 



The Strigine may, liowever, be distinguished from the Accipitrine girdle by the 

 following characters : — (1) The preacetabular ilium has the middle of its inferior border 

 deeply emarginate, so that a line drawn from the cephalic end of the emargination 

 inwards and for^vards to the point where the superior border intersects the vertebral 

 column, cuts off a large triangular segment of the innominate. (2) The dorsal plane of 

 the postacetabular ilium is continued forwards and outwards to form a conspicuous shelf 

 overhanging the acetabulum. (3) The ischium is continued backwards into a point along 

 the pubis. (4) Tlie pubis is always complete. 



The jireacetabular ilia never meet one another directly above the neural spines of the 

 lumbar vertebra?. In Gymnoscops, e. g. G. insularis, the two preacetabular ilia rise to 

 the level of, and just succeed in touching, tlie crest of the neural spine of the 1st 

 lumbar vertebra. By this a pair of conspicuous canales ileo-lumbales are formed. In the 

 majority of the Striges the hinder openings of these canals are much restricted by the 

 greater backward extension of contact between the neural spines of the vertebrae and 

 the superior iliac crest. In many cases the ilia are really rather widely separated, {he 

 canal being roofed by lateral expansions of the crests of the neural spines which extend 

 outwards to fuse with the ilia. In many genera, e. g. Asio, Bubo, Nyctala, Strix, the 

 canals are closed posteriorly, and thus become converted into cavcB ileo-himhales dor sales. 

 The postacetabular ilium lodges a fairly large iliac pocket. 



The pre- is about twice as long as the post-acetabular ilium, and the latter, it should be 

 noted, is not sharply deflected as in the Accipitres. Ihe fovea lumbalis differs from that 

 of many Accipitres in that, owdng, probably, to the relatively shorter neural spine, the 

 vertebral column lies within the fossa. In the Accipitres, the vertebral column projects 

 beyond the margin of the cavity, and is plainly visible when the skeleton is viewed from 

 the side. The fovea ischiadiciis is of considerable size, lofty, and strongly defined. Clearly 

 defined limits are not so characteristic of the fovea i^udendal is. This region can best be 

 studied in Si/rninm, where a lofty chamber divides the sacrum from a well-defined lylanum 

 coccygeum. Generally this chamber is obscured by the close approximation of the sacral 

 and caudal vertebrae, the ribs of the one, and the paraphyseal bars of the other, cutting 

 the chamber up into a number of compartments. The iliac recess is well developed in 

 all the Owls. 



The pelvic girdle of the nestling is instructive. At this stage the preacetabular is 

 more than twice the length of the postacetabular region, and the neural spines of the 

 lumbar vertebrae are low and project above the innominate. 



A feature of especial interest is the part played by the postacetabular ilium in the 

 formation of the iliac recess. If the innominate be removed from the synsacrum, it will 

 be seen that the mesial border of the postacetabular region curves inwards and down- 



