1894.] ox THE FLEXOn MTJSCLES IN BIRDS. 495 



2. On the Perforated Plexor Muscles in some Birds. 

 By P. Chalmers Mitchell, M.A., F.Z.S. 



[Received May 30, 1894.] 



However opinions may differ as to the value of muscles in 

 classification, t'ew would dispute that the ambiens muscle of birds, 

 in the peculiarity and isolation of its position and course, and in 

 the constancy of its relations, is an anatomical character ditticult to 

 overlook in classification. The ambiens, as all anatomists know 

 from the researches of Garrod, is a slender muscle wliich, after 

 origin from a spine or ridge immediately in front of, or below, the 

 acetabulum, runs along the inner side ot the thigh to end in a thin 

 tendon which usually crosses the knee and joins the Jtaavr 

 perforatus dicjitorum. Its presence and absence are associated 

 with so many other peculiarities of structure that Grarrod divided 

 all birds into the Ilomalogonatce, which possess the muscle in 

 question, and the Anomcdogonatce, in which the ambiens is absent. 



While taking advantage of the abundant opportunities afforded 

 by the laboratory iu the Society's Gardens, by the kindness of my 

 friend Mr. P. E. Beddard, the Society's Prosector, I have dissected 

 the leg- and thigh-muscles in tlie following birds : — 



Balearica cJiri/sojyclai'ijiis. 

 Halia 4us Inicofj aster. 

 Psophia leucoptera. 

 Th'iumalea amherstice. 

 Fulica leucopteru. 

 Leptoptilas crumeiiiferus. 

 Palamedea cornuta. 



Aramides ypecaha. 

 IJwin atojius ostra lee/ us. 

 Niicticorax cjardeni. 

 Edectus roratiis. 

 Corvus capellaims. 

 Buho maxhnus. 



In the first nine of these the ambiens is present, and the relation 

 of its tendon to the flexor perforatus digitorum is constant. In 

 these, as in other birds which I have dissected, the perforated 

 flexors lie immediately under the two " perforated and perforating" 

 flexors, those of the second and third digits. Fig. 1 (p. 496), which 

 I have drawn from a dissection of the Cape Crowned Crane, shows 

 an arrangement which is, in the main, typical of the other eight 

 birds. Distally, the three tendons pass respectively to the second, 

 third, and fourth toes. These tendons arise from a mass of 

 muscle innervated by that branch of the ischiadic nerve that also 

 supplies the middle head of the gastrocnemius muscle. The mass 

 of muscle has three distinct origins — an inner head, which arises 

 from the intercondylar notch very close to, and sometimes in 

 common with, the head of the flexor longus hallucis ; an outer 

 head, from the outer condyle of the femur under and partly in 

 common v^'ith the origins of i\iQ flexores perforuti et perforante^, and 

 from which a strong fibrous connection, sometimes double, runs to 

 the short arm of the biceps sling ; and an ambiens head, sometimes 

 fleshy, sometimes tendinous, from the tendon of the ambiens. From 



