Musculi Caudae et Cloacae - Annotations
The most recent, comprehensive, topographical description of the entire tail apparatus, in Columba livia, including a functional analysis of the movements of the entire tail and its appended flight feathers, is that of Baumel (1988). Other descriptive material is given in Vanden Berge (1975); Bentz (1983); Zusi and Bentz (1984); and Raikow (1985a).
(65) M. levator caudae may consist of two parts, Pars vertebralis and Pars rectricialis, differentiated on the basis of insertion. The proximal fasciculi attach on Proc. spinosus of the most caudal vertebrae; the distal fasciculi attach on the rectricial bulb, including the follicles of the major coverts and rectrices.
M. lateralis caudae inserts on the superior and lateral surfaces of the collar of the follicle of the outermost rectrix (e.g., rectrix 6 in Columba livia, Baumel, 1988). See Fig. 6.10A.
M. depressor caudae. M. depressor caudae is the ventral counterpart of M. levator caudae in general structure, position, and function, and is named accordingly. Three separate subdivisions, Pars proximalis, P. distalis, P. profunda, are described in Columba livia (Baumel,1988). A large proportion of the tendon fascicles of Pars proximalis from each side decussate obliquely to form an interwoven construction, Aponeurosis cruciata, which Baumel named, illustrated, and characterized functionally. This aponeurosis serves as an attachment for the ventral, extrinsic musculature of the tail, in particular for M. pubocaudalis internus (Annot. 66) and M. caudofemoralis, Pars caudalis (Annot. 110). Pars distalis attaches partly on the cruciate aponeurosis and partly in the rectricial bulb. Pars profunda attaches on the most caudal vertebrae and pygostyle. The hypaxial depressor caudae is more complex in structure than its epaxial counterpart; see Fig. 6.10B.
According to Baumel et al. (1990), these three intrinsic muscles are functionally non-ventilatory.
(66) M. pubocaudalis externus; M. pubocaudalis internus; M. caudofemoralis, pars caudalis. These muscles (see also Annot. 110) comprise extrinsic ventral musculature of the tail; see Fig. 6.10A. The name "pubocaudalis externus" or "internus" is particularly appropriate because it conveys information concerning (1) the principal origin (pubis; caudal margin of pelvis), (2) insertion (on tail structures) and (3) topographic position of these two muscles relative to each other. Both are also important structural components of the lateral abdominal wall. All three muscles are functionally expiratory during ventilation movements (Baumel et al.,1990). M. pubocaudalis internus is digastric, consisting of Pars pelvica and Pars caudalis, each part having an independent innervation, but separated by a tendinous intersection (Fig. 6.10). Fascia of pubocaudalis internus is continuous with Membrana iliocaudalis (Arthr. Annot. 185) and Septum supracloacale (Annot. 68), medially, and with Aponeurosis cruciata (Annot. 65).
(67) M. bulbi rectricium; M. adductor rectricium. M. bulbi rectricium is a striated muscle that ensheaths a well-organized fibro-adipose mass known as the rectricial bulb. M. adductor rectricium, on the other hand, is a non-striated muscle associated primarily with the inner aspect of the ventral elastic ligament of the rectrices; it supplies slips of insertion to rectricial follicles. See Fig. 6.10A and Baumel (1988).
(68) Musculi cloacales. A collective term for those muscles which interdigitate in the wall of the proctodeum and the vent, including also Septum supracloacale, the membranous partition from the inferior surface of the uropygium. See Cloaca Annot. 26, and Baumel (1988) for description of their functional roles.
M. sphincter cloacae (Cloaca, Annot. 27) is an intrinsic striated muscle of the cloacal wall, extending into the dorsal and ventral lips bordering the external opening or vent, its fascia continuous with Septum supracloacale. The dorsal sheetlike portion bridges the space between the tendinous intersections of M. pubocaudalis internus and is typically better developed than the subcutaneous ventral portion. See Fig. 6.10A. M. sphincter cloacae is also the hypertrophied muscular element of the phalloid organ in the Buffalo Weaver, Bubalornis albirostris (Bentz, 1983).
M. transversus cloacae (Fig. 6.12A, and Cloaca, Annot. 28) may consist of one or two separate heads of origin and/or separate bellies in some taxa, e.g., Apodiformes (Zusi, pers. comm.; Vanden Berge, pers. observ.). It originates mainly from fascia of limb muscles attaching on the caudal aspect of the pelvis, but also from the ischium and pubis, and the iliocaudal membrane (Arthr. Annot. 185) (Baumel,1988; Zusi and Bentz,1984). The muscle passes lateral (superficial) to M. pubocaudalis externus and M. pubocaudalis internus, with which it is closely related both topographically and functionally (expiratory ventilation: Baumel et al.,1990). It inserts into the fascia of M. sphincter cloacae above and below the vent of the cloaca.
Septum supracloacale (Baumel,1988). This is a membranous partition which (1) separates the dorsal wall of the cloaca, the duct from the cloacal bursa, and the dorsum of the bursa, from (2) the inferior surface of the uropygium. It is derived from a prolongation of the upper and lower fasciae of M. sphincter cloacae, and includes attachments with the tendinous intersection of M. pubocaudalis internus (Annot. 66), and M. sphincter cloacae.
For additional information on other cloacal muscles, see M. contractor cloacae (Cloaca Annot. 29); M. depressor anguli venti (Cloaca Annot. 30); M. levator cloacae [M. retractor phalli caudalis] (Cloaca Annot. 31; Masc., Annot. 51) ); M. dilator cloacae [M. retractor phalli cranialis] (Cloaca Annot. 32; Masc. Annot. 51).