Embryos and Nestlings o/Centropus sineusis. 663 



(fig. ]), except by means of the still persistent triclio- 

 ptiles, but originates at a point about midway between 

 the mid -dorsal line and the articulation of the liumerus^ 

 from here it runs up to and over the point of the 

 shoulder to fuse with the pt. ventralis; it is also con- 

 tinuous with the tectrices marginales but not with the 

 parapteron. The sheaths^ which are long and still pro- 

 vided with trichoptiles, are arranged in three rows deep. 

 The distance between this tract and the following is 

 much greater than formerly. 

 Pt.fe?noralis (fig. 4, pt f.). — A glance at the diagram will 

 show the peculiar nature of the tract at this stage : it is 

 plainly divisible into two portions^ a pre-axial and a 

 post-axial ; the former is rather indistinct, arising from 

 the pt. spinalis it runs obliquely upwards for a very 

 short distance ; the latter is not connected with the 

 spinal tracts its base-line is of considerable length, the 

 lower extremity sweeping down past the pygidium and 

 not far separated from the lower extremity of the inner 

 branch of the pt. ventralis ; from this base-line the 

 feather-sheaths rapidly converge and run over the out- 

 side of the thigh, mostly on its post-axial half. The 

 greater extent of this tract in younger stages is shown 

 by the trichoptiles. 

 Pt. cruralis has not altered in shape or size, though its 

 pre-axia"> uorti^n has lost its connection with the 

 pt. femoralis owing to the reduction of that tract. 

 Pt. ventralis (fig. 5, p. 661 ,pt. v.) . — This is now well developed 

 and dense. Commencing as a continuous tract between 

 the mandibular rami [cf. ante), it divides at the junction 

 of the head and neck into two broad main stems; these run 

 down the sides of the neck and chest for some distance, 

 when each stem re-divides into two branches — an outer, 

 short branch *, so short, in fact, that it hardly appears 

 to be a branch at all ; and an inner, narrow branch, which 

 runs down almost to the level of the anus, diverging 

 slightly from its fellow on the opposite side. The 

 * This branch ij :-aid to be very short in Rhinococcyx, 



