Wyman.] 260 [June 5, 



may be readily determined, for tliof:e parts willhe homotijpes ivJdch have 

 the same relalice position, and are si/mmetricall)/ placed ivith regard to 

 each other. 



Scapular and Pelvic Arches. The general homology of these has 

 attracted less attention than the determination of the corresponding 

 parts of the two with each other. Oken, Spix and Carus, considered 

 them as ribs, and in this respect have been followed by Owen, who 

 lias presented his views with much more precision than his predeces- 

 sors. Admitting them to be specially modified ribs, to what vertebrae 

 do they belong ? The pelvic arch has been assigned with much 

 unanimity to the sacral vertebras in the immediate neighborhood of 

 which it always is ; but the scapular arch offers a much more difficult 

 problem, since in the three higher classes of vertebrates, the vertebrae 

 near which it is found are all provided with ribs, and in many animals 

 all the cervical vertebrae are rib-bearing, independently of the arch 

 in question. Spix, who has been fbllowed by Owen, regards this as 

 being made up of the ribs of the occipital vertebra, and Owen urges 

 in confirmation of this view, that in fishes the scapular arch is an ap- 

 pendage to the occiput. 



The objections to this view, though we are not sure but that they 

 are more apparent than real, are, first, that in only one of the four 

 classes of vertebrates, viz., fishes, would the arch be found, so to speak, 

 in its normal place ; second, each such rib in the larger portion of the 

 vertebrate series higher than fishes, Avould be provided with two "car- 

 tilages" or "haemapophyses," viz., the coracoid and clavicle. This same 

 difficulty presents itself in connection Avith the pelvic ribs, since these 

 would also have two cartilages, the ischium and pubes. Third, the 

 objection urged by Agassiz appears to have much weight. He objects 

 that this arch and the limbs supported by it, derive their nerves in all 

 classes from the spinal, not from the cranial series, while the reverse 

 should be the case if they were truly cranial ribs. A branch of the 

 vagus, or of the lateral nerve formed by the union of the vagus and 

 trigeminus is, it is true, distributed to the scapular arch in addition to 

 its spinal pairs. This, however, would not make the scapular arch an 

 appendage to the head, any more than it does the trunk or even the 

 tail to which this same nerve sends branches in fishes and Urodel 

 batrachian reptiles. 



In view of these objections one cannot but feel that additional evi- 

 dence is needed, especially that to be derived from embryology, be- 

 fore definite conclusions can be reached. Extensive observations on 

 the development of the scapular and pelvic arches may be expected to 

 throw much light upon this problem. We have studied the develop- 

 ment of the pelvis in frogs, and find that this does not take place after 

 the manner of ribs. In the tadpole of the BuU-ti-og {Rana pipiens, L.) 



