268 



AMERICAN TESTUDINATA. 



Part II. 



pelvis with the femur, withdrawn under that large bony roof, though the ribs do 

 not extend over the jielvis as they do really over the whole shoulder apparatus. 

 As we have already seen, in the preceding section, that this bony roof is formed 

 of the ossification of the skin, it is plaiii that the position of the four limbs, 

 below its spreading margins, does not alter their homologies, and that on the 

 whole the locomotive members occupy here, as in all quadrujjeds, a normal posi- 

 tion upon the sides of the backbone, and that they are as usual protected by 

 the general covering of the body, only that here this outer envelope is ossified. 

 It follows, therefore, that Testudinata cannot form a class by themselves. The 

 shoulder is composed of three narrow bones, rather long and sti'aight, meeting in 

 one point, and forming at their junction the cavitas glenoidahs for the humerus. 

 Two of these bones, soldered together at right angles^ as one bone, represent, 

 the upper one, the scapula, the lower, the furcula of the Birds ;^ the third bone, 

 running backwards, answers to that bone in Birds which, coming from the scapula, 

 rests in a deep, transverse socket of the sternum. Merely to use names already 

 adopted, and without intending to homologize these bones beyond the limits here 

 alluded to, we shall call the first, scapula, the second, acromion, and the third, 

 coracoid process. The scapula, a long, cylindrical bone, is attached by a ligament 

 to the dorsal column just before the first (rudimentary) rib ; the acromion, a shorter, 

 somewhat flattened bone, is attached to the sternum by syndesmose just before the 

 odd bone. The coracoid process runs backward and hangs free between its mus- 

 cles; its broad, flattened posterior end, and the end of the acromion, are connected 

 by a strong ligament. This coracoid corresponds in its form and in its relations 

 to the other bones of the shoulder apparatus, though not in its attachment to 

 the coracoid of the Saurians, the Crocodiles, and the Birds, in all of which its 



' There is only one exception known to this gen- 

 eral rule. In a skeleton of a North American Emys, 

 in the Anatomical Museum of Berlin, there is on one 

 side of the animal a suture between these two bones. 

 See Stannius, Handbuch der Zootomie, I., 2d edit., 

 p. 75, note. 



"^ There has been much diversity of opinion about 

 the homology of the three bones of the shoulder 

 apparatus of the Turtles, and the two or three bones 

 which we find in their place iu other Vertebrata. 

 Bojanus, in his great work, Anatome Testudinis Ym- 

 rop<B£e, VilnsB, 1819, at first mistook the coracoid for 

 th(^ scapula, and called clavicula the scapula, together 

 with the acromion (see PI. viii., O and N) ; but he 

 soon afterwards corrected himself in the Isis. Cuvier, 



and most anatomists now living, Stannius, among them, 

 in the second edition of his Handbook, have named 

 these bones as we do, while in his first edition, p. 139, 

 Stannius called the acromion, clavicula. Dumeril 

 and Bibron (Erpetologie generate, I., p. 382) call the 

 coracoid, clavicula. We see here that for each bone 

 nearly all possible homologies have been supported 

 by some writer or other. This seems to show that 

 there are limits to horaologizing. Though we are 

 persuaded that these bones of the Turtles are homol- 

 ogous to those of tlie Birds in the manner in which 

 we have referred them, one to the other; yet we do 

 not dare to go farther, and liomologize them at the 

 same time with tlie bones of the shoulder in Mamma- 

 lia, and still less with the thoracic arch of Fishes. 



