43 INTRODUCTION. 



this element distinct in a dog ; the senior author has observed (19, 301, 

 Fig. 1,) it as a separate center of ossification in a young lion, shown in 

 Figure 47 ; and it is apparently shown, though not alluded to, by Mivart, 

 (B, Fig. 60.) 



There are many interesting and important questions connected with the composition 

 of the carpus and tarsus of different Vertebrates, and those interested in the subject 

 may consult Gegenbaur (Lankester), A, 479-481, 487, 488, and the papers of that anato- 

 mist, Morse (18 and 1) Marsh {!), and Wilder [Id). 



§ 86. The metapodials are comparatively simple elements. In the 

 diagram, the pollical (first) metacarpal is made shorter than the rest, as is 

 the case in the cat, and the primal (first) metatarsal is represented as a slight 

 rudiment, the reniainder of it and the whole dactyl being absent, and hence 

 shown by dotted lines. 



The ordinary digits and dactyls have each three phalangeal segments, 

 proximal, intermediate, and distal. The pollex has but two, and in those 

 Mammals which have a primus, this usually consists of but two phalanges. 



§ 87. This peculiarity of the pollex and primus has always constituted a main argu- 

 ment in favor of the prevailing view as to the correspondence of the limbs with each 

 other — inter membral homology/. 



According to this view, the cephalic borders of the arm and leg correspond, morphi- 

 cally as well as telically ; the radius is the homologue of the tibia, and the ulna of the 

 fibula ; and the pollex is both the homologue and the analogue of the primus. 



This, the syntropical idea of intermembral homologies, has been adopted, in one form 

 or another, by nearly all anatomists. 



The other idea, that of antitropy, has been advocated or accepted by a much smaller 

 number, including the elder Agassiz, Coues, Dana, Poltz, Wyman, and the senior author. 



According to this view, the two ends of the soma, and thus the cephalic and caudal 

 aspects of the limbs, are reversed or symmetrical repetitions of one another, as are tlie cor- 

 responding organs upon the right and left sides. The radius thus becomes the homologue 

 of the fibula, and the tibia of the ulna, while the poUex represents the quintus, and the 

 minimus the primus. 



Fully recognizing the apparent objections to this view, we nevertheless believe it to 

 be correct, and would refer those interested in the subject to the paper (10) by the senior 

 author, where these objections are discussed and the opinions of other writers stated, 

 with a List of Works and Papers treating of the general question. 



§ 88. Enumeration of Parts in a Series.— As has been stated (§ 30, 

 79), two or more similar parts which form a series are enumerated in order, 

 beginning with the one nearest the head, or the meson, or the proximal end 

 of the more comprehensive part of which they are subdivisions. 



On the diagram (Fig. 6) are given some illustrations of this method. 

 The vertebra have been referred to already. Of the digits and dactyls, the 

 most cephalic in each series may be designated as the first ; but it is evident 

 that this might cause confusion in the case of animals having only four 

 or a less number of fingers or toes. 



