18i)7.1 2G1 [Wyman. 



tlic fii'st trace of the pelvis consists of a plate of cartilage situated 

 on the median line in front, and which corresponds in jwsition with 

 the future ischium and pubes. This cartilage subsequently becomes 

 extended on either side, and at last forms a connection with the trans- 

 verse processes of the sacral vertebrae Its first stage, it will be seen, 

 corresponds very nearly with the permanent condition of the pelvis in 

 most fishes. In Cetaceans, the pelvis consists of ischia, or ischia and 

 the bones of the pubes alone ; the ilia do not exist. This would seem 

 to be an indication that in mammals the development of this part 

 followed the same course, as in frogs and fishes ; that is, it begins its 

 development on the median line in front. 



In most vertebrates the special homology of these arches is more 

 obvious, though somewhat masked, since the physiological require- 

 ments of the two differ go widely ; strength antl solidity being essen- 

 tial conditions in the pelvis and mobility in the shoulder. If, how- 

 ever, they are compared in those animals whose habits are moi'e 

 strictly aquatic, and whose locomotion is eifected more nearly equally 

 by the fore and hind limbs, as, for example, in the Onrithoi-Jtipichus 

 among mammals, and the marine saurians among reptiles, the scapular 

 arch, in consequence of the greater development of tlie coracoids, and 

 of the union of these as well as of the clavicles with the sternum, or with 

 each other, will be found to have almost the firmness of a pelvis. On the 

 other hand the attachment of the pelvis to the vertebral column may 

 become comparatively slight. In the chameleon the pelvis is nearly 

 as moveable as the scapular arch, and in the Icthyosaurus it appears 

 to have been entirely free, and to have embraced the ribs behind as 

 the scapular arch does in front. (See Cuvier's Oss. Foss. PI. 260.) 

 Although the two arches never repeat each other exactly in one and 

 the same animal, they do sufficiently to show that they are constructed 

 upon one and the same plan. The scapular arch of one animal, how- 

 ever, often very nearly resembles the pelvic arch of another, as, for 

 example, the first taken from a frog. Fig. 7, when compared with the 

 second taken from a chameleon. Fig. 8, but in the Enaliosaurians the 

 resemblance of these parts in the same individuals is still more 

 striking. 



As each arch consists of three pieces, the first step is to determine 

 which are the corresponding ones. Vicq d'Azyr comparing bones 

 from opposite sides, Gerdy, Bourgery, Blandin, Flourens, Cruveilhier, 

 and Owen* comi^aring those of the same side, agree in considering the 



* "I commence with ilium as being the homotype or correlative of the scapula in 

 the fore limb. The ischium, which is the homotype of the coracoid, is coufluent 

 with tlie ilium, as the coracoid is with the scapula; the pubes, which is the homo- 

 type of the clavicle, is confluent with both ilium and ischium." Philos. Trans., 

 1859, p. 809. 



