178 MR WM. TURNER ON VARIABILITY IN HUMAN STRUCTURE. 



specialisation occurs both in internal structure and external form, by which dis- 

 tinctive characters are conferred, so that each man's structural individuality is an 

 * expression of the sum of the individual variations of all the constituent parts of 

 his frame. 



But it is not essential that, for the demonstration of this specialisation of 

 structure in the individual, "\ve should extend our inquiries over all the organic 

 systems. Any one, if carefully examined, will afford us sufficient evidence of its 

 existence. The muscular system is the one I have especially selected for illustra- 

 tion. There are some parts of this system in which, from the mode of arrangement 

 of single muscles, and from the manner in which they are collected into groups, 

 we are enabled to study more precisely than in other localities the extent of varia- 

 tion which is permitted, and the various forms which it assumes. None are 

 better fitted for this purpose than the flexor muscles of the fingers and toes ; for 

 not only can we define with great exactness the arrangement of these muscles and 

 their tendons, but we can employ in connection with them a method of descrip- 

 tion precise enough to convey a conception, not only of the stronger and best 

 marked varieties, but of the more minute deviations from their usually recognised 

 disposition. During the past twelve months, I have made a series of special 

 dissections of these groups of muscles, and I shall now record the general results 

 which I have arrived at in the examination of these parts. It must be under- 

 stood that all the dissections were made on the bodies of the inhabitants of these 

 islands, natives of either Great Britain or Ireland. 



The flexor muscles in the forearm and hand, to which my attention has 

 especially been directed are the flexor longus pollicis, the flexor sublimis 

 digitorum, the flexor profundus digitorum, and the lumbricales. The long flexor 

 muscles exhibited numerous variations in their bulk, in the extent of their 

 attachment to the bones of the forearm (the extent of the radial origin of 

 the superficial flexor was especially variable), and to the interosseous or 

 other fibrous membranes from which they arose. The superficial and deep 

 flexors of the fingers also varied as to the mode in which they divided into their 

 terminal bundles ; in some cases the division took place lower down in the fore- 

 arm than in others. This was especially the case with the deep flexor, in which it 

 was not unfrequent to see the separation between the more internal of its 

 terminal tendons still incomplete at the carpal end of the forearm, or beneath 

 the annular ligament. In one specimen in my possession, the muscle divided into 

 five bundles, two of which afterwards united to form the tendon for the ring 

 finger.* But, in addition, other variations were met with of a more remarkable 



* Multiplication of the bundles of tin's muscle has been recognised by Arnold, Henxe (Mus- 

 kellehre, p. 196, 1858), and Theile (Traite de Myologie), 1843, p. 246. Theile also states that 

 it sometimes receives a special head of origin from the inner condyle of the humerus ; and Theile, 

 Hallett (Ed. Med. and Surg. Journ. vol. lxxii. p. 12), and Henle state that it sometimes receives 

 fibres from the radius. 



