126 THE BONES. 



digital section, and two rudimentary pieces on each side of it, and which are 

 really atrophied metacarpals ; for in some teratolo.^ical specimens they are as long 

 as the principal bone, and terminate in a diarthrodial surface which articulates 

 with a perfect digit (Fig. 82, l b). At first sight, there are, then, three meta- 

 carpals in Solipeds. 



With several authorities, and particularly Joly and Lavocat, we have 

 admitted the duplicity of the large median metacarpal bone, basing our admis- 

 sion on several considerations with regard to form and relations, and especially 

 on certain anomalies similar to those represented in Fig. 82, i, in which 

 is seen the single digit of Solipeds divided like that of the Ox — the division 

 extending to the lower end of that bone. But an attentive study of the 

 metacarpal region in the Mammalia, and notably in Pachyderms, and of the 

 arrangement it offers in the various fossil Equidae, has caused us to abandon 

 this opinion. We consider the principal metacarpal of Solipeds to be the analogue 

 of the metacarpus of the medius of pentadactylous Mammals. With regard to 

 the anomaly shown at i and K, Fig. 82, it should be interpreted as an example 

 of division of an organ normally single. 



The Horse, then, has always three metacarpals — one for the medius, the 

 index, and the annularis ; and it remains to prove the existence of two other 

 metacarpals. Usually, the metacarpal of the thumb is completely aborted ; but 

 yet the existence of these bones is indicated by the frequent presence of the 

 trapezium at the inner side of the carpus. Lastly, as a continuation from the 

 trapezium there may be found a conical prolongation (Fig. 82, l a, 5), parallel 

 with the metacarpal bone of the index — a prolongation which, because of its 

 connections, should be regarded as the metacarpal of the thumb. 



With respect to the metacarpal of the auricularis, or little digit, we do not 

 know of one teratological example in which it can be distinctly seen. But its 

 existence is virtually indicated by the presence of the small external carpal bone 

 we have sometimes observed, and which was noted by Bourgelat, Eigot, and 

 Goubaux. 



The phalangeal section only possesses the elements of a single digit. But 

 besides the hoof, Soliped animals have a horny plate divided by a slight median 

 groove, and resting on an elastic cushion behind the metacarpo-phalangeal articula- 

 tion. This plate occupies the same position as the ergots in the Ox : it has vessels 

 and nerves from the same source as those of the principal digit ; it lies upon an 

 elastic bed similar to that belonging to that organ ; and Joly and Lavocat regard 

 it as the representative of the phalanges, which should be continued with the 

 rudimentary metacarpals. Otherwise, when one of these metacarpals is developed 

 into a perfect digit, the horny plate or ergot diminishes in volume, because 

 a portion of its substance is carried to the extremity of the supplementary digit. 

 It is, therefore, easy to find three digits in these animals, but the thumb is more 

 difficult to render evident. However, the presence of a trapezius, and, much 

 more rarely, of an atrophied metacarpal succeeding it, would warrant the admis- 

 sion that this digit exists, if it were not represented on the surface of the skin by 

 the chestnut — the horny plate situated on the internal aspect of the forearm. 

 The position of this small mass of horn above the carpus has been invoked 

 against this signification : but it is easy to overcome this objection in showing, by 

 the ascending vessels and nerves of the chestnut, that this is a displaced organ ; 

 the vessels and nerves arise from the same trunks that supply the other digits. 



The fifth digit is not absolutely represented except by its carpal base, which is 



