MUSCLES OF THE HIND LIMB 103 



Flexor secundus (adductor) digiti IV. is a muscle which 

 appears to be generally absent (e.g. Giconia), and is not, 

 according to Gabow, mentioned by authors. It is present 

 in Rhea and Bucorvus. 



The last-named muscle may be the equivalent of the 

 first of the two short flexors which arise from the deep long 

 flexor tendons. Of these there are two. 



(1) Mitchell has described in Opisthocomus a muscular 

 slip which leaves the longus hallucis tendon and runs to the 

 fourth digit. A similar muscle is present in Ardea cinerea ; " 

 I have found it in the hornbill, Ceratogymna elata (not in 

 Aceros nipalensis) . 



(2) Another muscle {flexor brevis digiti III. of Gadow) 

 arises from tendon of flexor prof undus in Opisthocomus, Bhea, 

 &c., and passes to third digit.'-* 



Of short extensor muscles there are at most six. 



The extensor hallucis, generally single, is two-headed 

 in Pandion, and formed of two distinct muscles in Pala- 

 medea. 



The extensor proprius and extensor brevis digiti III. both 

 supply the third digit. In Aceros and Bucorvus a single but 

 two-headed muscle appears to represent both. 



The extensor (adductor) digiti II. is not always present. 



The same may be said of the extensor digiti IV. 



Muscles of the Neck and Trunk 



These muscles are, many of them, not easy to isolate and 

 describe. There is, in consequence of this, some divergence 

 in the published accounts. Furthermore, insufficient data 

 have been collected for the estimation of the use of these 

 muscles in classification. The account which follows is an 

 almost verbatim transcript from a paper upon Palamedea^ 

 by Mr. Mitchell and myself. ^ 



' It is suggested by Mitchell that these muscles (which require further 

 study) may ' throw light upon the origin of the very peculiar modes of distribu- 

 tion of the hallucis tendon in some groups of birds, as it has been repeatedly 

 shown that a tendon may be the homologue of a muscle.' 



' Gaebod MS. " Quoted on p. 108. 



