15(5 



digitorum brevis pedis and extensor digitorum longus. The first of 

 these muscles in the upper limb has a condyloid origin, which in the 

 lower limb is obsolete, as the condyle itself is diminished; it has a 

 second or radial origin above the flexor pollicis muscle which is altered 

 in its connexion, and appears in the leg as the external head of the 

 solaous. These parts being altered, and the power of the muscle being 

 much diminished, it is contracted into a foot muscle, and the same 

 change has occurred to all its tendons, which I have described above as 

 occurring to the indicial one of its hand representative, and they all are 

 made by the suppression of the upper part to assume a tarsal origin, 

 the insertion and its mode of perforation remaining constant. The 

 extensor muscles of the hand and foot are the undoubted exponents, the 

 one of the other ; and as the pollex has a series of differentiated actions, 

 we have its extensor separated from the rest of the mass, as the extensor 

 primi internodii pollicis, and thrown back a step. There is no flexor 

 of this series for the pollex. Similarly, we have an extensor for the 

 hallux, the extensor primi internodii rarely developed, and retrograde 

 one step in insertion from non-development of the second phalanx, and 

 no proper second flexor of this group in man. 



The third series of digital muscles are the flexors and extensors of 

 the third phalanx of each finger and toe. We find these represented 

 by the flexor profundus perforans manus and flexor pollicis above, and 

 the flexor digitorum longus perforans pedis and flexor hallucis below. 

 Now, in comparing these muscles in the lower limb, it will be seen that 

 the muscles cross each other, the flexor hallucis taking a fibular (ulnar) 

 origin, and passing outwards, while the flexor digitorum arises on the 

 tibial (radial) side, and passes inwards. Now, no crossing takes place 

 in the upper limb, but we find it in the lower limb, as an index of the 

 change which has taken place in the bones of the extremity; and as 

 these muscles are but the differentiated portions of one layer, it is not 

 surprising that constant unions are taking place between their tendons 

 at the point of crossing. This seems a more natural explanation, con- 

 sidering the position of the limb bones, than the idea that the flexors had 

 exchanged tendons, and what should be the flexor pollicis muscle sup- 

 plied the other toes, and vice versa — a theory which cannot be sustained 

 on teleological or embryological grounds. All these muscles seek 

 insertion into the last phalanx ; their corresponding extensors are but 

 poorly developed. "We have certainly the extensor secundi internodii 

 pollicis, the rudiment of the muscle for this finger, and the extensor 

 proprius pollicis, the fully developed muscle for the great toe ; we 

 have the extensor indicis of man as the second extensor unrepresented 

 in the foot ; the extensor medii digiti manus likewise unrepresented in 

 the foot ; the extensor quarti digiti either an offshoot from the extensor 

 minimi digiti, as in monkeys, or as a deep forearm muscle, but still 

 typical in its insertion, find represented in the foot as peroneus quarti 

 metatarsi ; and lastly, we have the extensor minimi digiti typified in 

 the leg by the peroneus tertius, whose insertion is thrown back several 

 degrees. Recession of this kind, however, is to be noticed in many of 



