MORPHOLOGY OF THE OWLS, 27 



of forms varying between 5 and 6 jiairs, the last of which fail to reach the sternum. 

 Some species of Strlx {e.g. S. delicatula), Asio, Carine, Snrnia, Speotyto, Syrnium, have 

 five pairs, which articulate with the sternum, the sternal segment of the 6th pair being 

 generally bound by connective tissue wdth the lower fourth of the fifth corresponding 

 segment. In one skeleton of Stria;, however, in the Museum Collection (1223 a) the 

 sixth j)air articulates with an imperfect facet projecting from the lower one-third of 

 the fifth segment. Frequently only four pairs of ribs articulate with the sternum, the 

 fifth, or even fifth and sixth pairs having sternal segments too short to reach the 

 sternum. 



Various stages in the reduction of the number of the ribs are to be met with. Leaving 

 out of consideration the anterior thoracic (cervico-thoracic), we may have as many as 

 seven pairs of true thoracics. Of these not more than six pairs ever articulate with 

 the sternum, the seventh in some cases being quite long, the sternal segment almost 

 reaching the sternum, e. (j, Athene (1095 e). In others vestiges of the vertebral segment 

 only remain, e. g. Gymnoscops (94.11.10.1), or of the sternal segment only, e.g. Bubo 

 capensis (9S.6.8.2). The reduction of the 6th and 5th pairs proceeds in a similar way. 



There is evidence to show that at least nine pairs of ribs recently articulated with the 

 sternum. Of these the first and second pairs, by loss of their sternal segments, 

 have become transferred to the cervico-thoracic series ; whilst the last pair, by loss of 

 their vertebral segments, have become transferred to the lumbar series. In many species 

 the number of ribs has become, as we have already remarked, reduced to five pairs, of 

 which four pairs only articulate with the sterniim, the reduction taking place sometimes 

 from the anterior, sometimes from the posterior members of the series. 



The uncinate processes are well developed, but except rarely not more than five pairs 

 are present. Occasionally the last cervico-thoracic rib bears an uncinate, but the last 

 (7th) thoracic appears to have lost the appendages completely. They are long and 

 slender in shape, sloping obliquely upwards and backwards. They are relatively 

 longest in Strix, extending backwards on to the thii-d rib from their base of attachment. 



VI, The Pectoral Gikdle and Sternum. 



The pectoral gii'dle of the Striges is extremely uniform in character throughout the 

 group, and in certain characters bears a very close resemblance to that of the Falconi- 

 formes. 



As a whole the girdle of the Striges can be distinguished from that of the Buteonine 

 section of the Falconiformes by the presence of a prominent procoracoid process, and 

 from the Palconine section, in which a procoracoid process is present, by the smaller 

 relative size of the acrocoracoid, which in the Falconidte is large, and by the form of the 

 furcula. This, in the Striges, is relatively long and slender, only slightly curved dorso- 

 veutraUy, and is furthermore frequently incomplete, the limbs failing to meet in the 

 middle line. 



The pectoral girdle of the Striges can readily be distinguished from that of the 

 Caprimvdgi, in that in the latter group there is no procoracoid process, and the furcula 

 is strongly curved dorso-ventraUy. 



4.* 



