Part 9 (1/2)

INDIVIDUAL VARIATION.--The anterior edges of the two adductor muscles may be fused together. In one leg, the entire muscle is indistinguishably fused with M. adductor profundus and they appear as a single muscle.

=_M. Adductor Profundus_= (M. adductor longus et brevis, pars interna), Figs. 13, 15, 17, 18

_T. pallidicinctus_

GENERAL DESCRIPTION AND RELATIONS.--Broad; on medial surface of thigh immediately posterior to femur; bounded posteriorly by M. flexor cruris medialis (medial to anteroproximal corner of latter), anteriorly by M.

femoritibialis internus (anterior edge overlapped by latter), and laterally by Mm. adductor superficialis and femorocruralis; proximal end tendinous (except anterior edge), fused to proximal fleshy end of M.

adductor superficialis.

ORIGIN.--The muscle arises tendinously from the ventral edge of the ischium extending from the posterior border of the obturator foramen to the ventral ischiatic tubercle and (anterior edge) fles.h.i.+ly from the lateral surface of the pubis ventral to the obturator foramen; the origin is adjacent (ventral) to the origin of M. adductor superficialis.

INSERTION.--The attachment is fleshy and tendinous from the posterior intermuscular line and (proximally and distally) from a narrow adjacent area. Proximally there are often two approximately parallel lines a short distance apart, representing points of attachment of the lateral and medial edges of the muscle; if there is only one line proximally, it may represent the attachment of either the lateral or medial edge of the muscle; distally there is usually only one line, representing the lateral edge of the muscle. The distal end extends onto the posterior surface of the proximal part of the internal condyle, and is adjacent (lateral) to the origin of M. femoritibialis internus, adjacent (medial) to Mm. adductor superficialis and femorocruralis, and adjacent (proximal) to M. gastrocnemius pars media.

INNERVATION.--See M. adductor superficialis.

INDIVIDUAL VARIATION.--The anterior edges of the two adductor muscles are strongly fused together in some cases.

_T. cupido_

INDIVIDUAL VARIATION.--The anterior edge may be fused with that of M.

adductor superficialis. The distal end is sometimes slightly fused with M. gastrocnemius pars media. In one leg, the proximal two thirds of the insertion is entirely tendinous, whereas in another the distal end of the insertion is tendinous.

_P. p. jamesi_

INDIVIDUAL VARIATION.--The anterior edge (in one leg the entire muscle) in some legs fuses with that of M. adductor superficialis.

=_M. Obturator_= (M. obturator externus + M. obturator internus), Figs.

16, 17, 18, 19C, D, 20K, L, M

I am adopting the single name M. obturator for the complex that Fisher (Fisher, 1946; Fisher and Goodman, 1955) subdivides into Mm. obturator externus and obturator internus. The reasons for this change are given in the section on terminology.

For ease of description, it is desirable to apply names to the subdivisions of M. obturator. It has been customary to divide the obturator complex into two parts--an obturator internus and an obturator externus; the latter has often been further subdivided. The evidence given below demonstrates that a primary division of the complex into only two parts is unsatisfactory.

I strongly suspect that comparable parts of the obturator complex have been considered a part of the ”internus” in some birds and a part of the ”externus” in others. In their work on the Galliformes, Hudson, _et al._ (1959) subdivide the obturator complex into only two divisions--obturator externus and obturator internus. The extrapelvic part of this complex that arises from the rim of the obturator foramen and inserts in common with the stout tendon of the main intrapelvic part of the obturator internus is considered by them to be a part of the obturator internus. Their obturator externus lies anterior and deep to the extrapelvic part of the obturator internus and inserts separately from the latter. (I also have found this same arrangement in _Tympanuchus_ and _Pedioecetes_.)

Berger (1952), in his description of the Black-billed Cuckoo (_Coccyzus erythrophthalmus_), also divides the obturator complex into an obturator internus and an obturator externus; the latter he subdivides into a dorsal and a ventral part. He states (p. 530) that he did not find any measurable differences in myology between _C. erythrophthalmus_ and _C.

america.n.u.s_. In order better to compare this arrangement with that in _Tympanuchus_, I have examined two specimens of _C. america.n.u.s_. My findings in the latter differ from Berger's description (p. 541) in one respect. Whereas Berger states that the dorsal and ventral parts of M.

obturator externus are distinct except at their origin, I find them fused for their entire length; the muscle fibers that connect these two parts lie deep to the tendon of M. obturator internus. The origin of all parts of the complex in _Coccyzus_ is similar to that in _Tympanuchus_.

The only notable difference in configuration is that the part in _Coccyzus_ that appears to correspond to the obturator externus of Hudson, _et al._ (1959) is not separate from the remainder of the extrapelvic part of the muscle. Berger (1952) considers all parts of the muscle having an extrapelvic origin to make up the obturator externus.

It appears to me that the dorsal part and a part of the ventral part of the obturator externus of Berger correspond to the extrapelvic fleshy part of the obturator internus of Hudson, _et al._

From my limited study, it seems to me to be desirable to recognize four subdivisions of the obturator complex, for which I propose the terms pars antica, pars dorsalis, pars ventralis, and pars postica. These parts exhibit various degrees of fusion in different groups of birds and some parts appear to be absent in certain birds. A study of a wide variety of birds will be required to determine whether or not a subdivision into the four parts proposed here is suitable for birds as a whole.

Applying these terms to _Coccyzus_, pars postica is equivalent to the entire obturator internus of Berger (1952). Pars dorsalis is apparently equivalent to the dorsal part of Berger's obturator externus. The ventral part of the obturator externus of Berger represents the fused pars antica and pars ventralis.

The main parts of the obturator muscle appear to be pars postica and pars antica. Pars dorsalis and pars ventralis are more variable; in _Coccyzus_ these two parts are closely a.s.sociated with pars antica whereas in _Tympanuchus_ they are most closely a.s.sociated with pars postica. Apparently pars dorsalis and pars ventralis may be absent in some birds.