TRANSACTIONS OF SECTION D. 429 



8. Some Points in Manus and Pes of Primates. 

 By Professor R. J. Anderson, M.D. 



The development of certain fingers and toes in animal groups is now regarded 

 as the ultimate result of efforts to respond to 'changes of environment. Not only 

 in the more conspicuous examples of reduction in the number of the phalanges, 

 but even in man, there is evidence of a polydactyl ancestry. The modifications of 

 the limbs in Primates in order to meet the exigencies of life are illustrations of 

 the possibilities of modifying what some regard as fixed types. The modifica- 

 tions may rise here as in other groups from the encouragement given limb elements 

 to develop at the expense of their neighbours. The fourth finger and the fourth 

 toe of lemurs are longer than their neighbours, not merely in their collective 

 length but in the length of their constituent joints. The first metatarsal is longer 

 in the foot than the remaining ones ; in the hand the first metacarpal is not so long 

 as the others. Cheiromys and Galeopithecus present special modifications. Those 

 of the latter are outside the present note. The metatarsals of the fourth and 

 fifth toes in the ruffed lemur are nearly equal. The length of foot in Pithecia 

 is 11 cm., the length of hand is 7"5 cm. The calcaneus is much longer than 

 broad in Cercopithecus, less so in Hylobates Mulleri. The second metatarsal 

 is longest. There is a cartilaginous development, apparently, in the calcaneo- 

 scaphoid ligament and an os peronei is present. The navicular is in position 

 not unlike the scaphoid of the hand. The intermedium which is commonly 

 supposed to be united to the tibiale to form the astragalus may not be the 

 equivalent of the lunar of the hand, which may really be represented by the 

 posterior or outer part of the astragalus or the os trigonum (as seen in man). 

 The navicular commonly regarded as a centrale may be the equivalent of the 

 scaphoid in the hand, according to W. Krause. Then the astragalus could be 

 regarded as a lunar, and the astragalo-scaphoid of emys and the crocodile, and, 

 as found, on one occasion, in man, as equivalent to the scapho-lunar which is 

 found in carnivora and others. The breadth of the hand in Hylobates, across 

 the base of the metacarpals is 1'8 cm., and across the distal ends 2'4 cm. The 

 like measurements in the foot give 2-2 cm. in front and 2"4 cm. behind. In man 

 the varieties in the carpus and tarsus are in part due to causes or factors that 

 operate in other animals, as well as to factors that are called into play in 

 attempts to imitate. Reduction of the number by coalescence, or increase of the 

 number by the formation of new ossicles, may take place in both carpus and tarsus. 



The importance of the study of varieties of these is clear from a practical 

 aspect, as a variety may be taken for a fracture in carpus and tarsus. A separated 

 epiphysis may resemble a fracture, so may a sesamoid. It is interesting to know 

 that a very large number of varieties have been met with in the carpus in man. 

 It would be safe to say that man is the only animal in which so many (thirty) 

 varieties in the ossicles of the wrist occur. The number would be much larger 

 if cases of coalescence and sesamoids were added. It seems almost certain that 

 the power to imitate has led to the occurrence of bones in the wrist that have 

 never been found in other animals. The same may be said of the bones of the 

 tarsus, but there are not by any means so many as one might expect where the 

 degree of movement is curtailed and the power of imitation limited. Tarsus 

 varieties may exceed twenty. Coalescence of the talus and scaphoid is parallel 

 to the scapho-lunar arrangement in many animals; I have found the former in 

 man. It happens, indeed, that several variations are known. The os trigonum 

 tarsi, which is oftener in adult men than in adult women, was considered by 

 Hyrtl to be the broken off trochlear process of the talus. V. Bardeleben homo- 

 logised the bone with the os lunatum of the hand. 1 The origin is due to certain 

 mechanical factors that come into operation. The os trigonum is originally a 

 skeletal part equivalent to the intermedium antebrachii (os triangulare). The 

 size is 35 to 20 mm. by 10 to 15 mm. vertical. It lies behind the talus and 

 articulates with the calcaneum by cartilage, fibrous tissue, or a joint ; it may be 

 connected with the talus. If an articulation exists the joint communicates with 

 the talo-calcaneal. There are two parts of the posterior surface of talus, the 



> Professor Dwight has figured and described (Anat. Anzeiger) a secondary 

 calcaneum and a secondary cuboid. He had discovered the latter by Rfintgen ravs 

 skiagraph before cutting down. ' 



