322 M. Rathke on the Development of the Chelonians. 



beyond the adjoining parts of the skeleton, the first pair of ribs 

 and the scapulae, in the form of a dome. 



The position and articulation of the pelvis of the Chelonians 

 differ absolutely in nothing from the normal type which verte- 

 brated animals present as regard the relations of position of the 

 pelvian bones ; for the coxal bones of the Chelonians are joined 

 to the os sacrum as in the mammals and in the Saurians in 

 general. Thus they offer nothing in particular, except that they 

 are covered by other osseous parts. This covering, which we find 

 over the whole pelvis of the Chelonians, results in a small part 

 from an enlargement of the penultimate pair of the ribs, but 

 principally from the development of the cutaneous skeleton, for 

 almost the whole posterior part of the shield, forming in most of 

 the Chelonians a roof above and behind the pelvis, is composed 

 of osseous pieces, developed near the chorion and independent 

 of the vertebral column and the ribs. 



With respect to the fact that we find both the humeri and the 

 femora of the Chelonians covered above, and in some species also 

 more or less underneath, this is generally in consequence of the 

 longer or shorter lateral folds of the chorion, in which peculiar 

 osseous pieces belonging to the cutaneous skeleton are developed. 

 It is likewise owing to this, that of the eight pairs of intermediate 

 ribs very much elongated and directed outwards, the last two are 

 moreover turned greatly backwards, and in several Chelonians, 

 but* not in all, the two anterior ones forwards ; the former extend 

 beyond the coxal articulation, the latter beyond the scapular 

 articulation. 



These facts appear to me to demonstrate the error of the com- 

 mon assertion, that in the Chelonians the bones composing the 

 shoulder and the pelvis are within the body. The arrangement 

 of the peritoneum in the Chelonians proves it even in a positive 

 manner, for it does not envelope on the two sides any of the os- 

 seous parts of the shoulder nor of the pelvis with their muscles : 

 it clothes them only on a single side, that turned towards the in- 

 testines. Behind, it enters, as in the mammals, at a distance 

 in the cavity of the upper pelvis, clothes in part its internal sur- 

 face and the muscles which are fixed there, and passes thence 

 over the viscera placed in this pelvis. Finally, it proceeds beneath 

 the dorsal part of the body up to the scapulse (situated, as I 

 have said, far anteriorly), enveloping the lower surface of the 

 kidneys, the internal genital parts, the inferior surface, and the 

 external margin of the lungs, with almost their whole upper surface 

 adhering to the ribs, and the portion of the ribs extending late- 

 rally beyond the lungs and the urinary organs. After having 

 passed the lungs, which reach in front the seapulse, over the 



