(1) Vas lymphaticun initiale (Fig. 13.1). Initial lymphatics always lie within organs and may be sinuses (lymph capillaries) or precollectors (see Annot. 4) (Konitz,

et aI., 1985; Berens v. Rautenfeld, et aI., 1987a).

(2) Sinus Iymphaticus initialis [Vas lymphocapillare]. The term "initial lymph sinus" (Fig. 13.1) characterizes this section of the initial lymphatics better than

"lymph capillary" (Berens v. Rautenfeld, et aI., 1987a; Castenholz and Berens v. Rautenfeld, 1987).

(3) Fibrae basilares; Fibrae iIxationes; Accessus interendothelialis; Ponticulus endothelialis. These structures are components of the "opening apparatus" (Fig.

13 .2) of the initial lymphatics which permit the influx of fluids from the interstitial space into the lumen of the initial lymph sinus. All of these components also occur in "precollectors" (Vas I. precollectorium) (Berens v. Rautenfeld and Wenzel-Hora, 1985; Berens v. Rautenfeld, et al., 1987a). Except for the Fibrae fixationes, the

elements in the heading of this annotation (Fig. 13.2) are not listed by the Nomina Histologica (NH) (1989). The components of the opening apparat\ls in birds, and

amniotes generally, are: (I) a wide-meshed subendothelial network of reticulin fibres (Fibrae basilares); (2) anchoring fIlaments (Fibrae fixationes); (3) interendothelial openings (Accessus interendotheliales); (4) and endothelial bridges (~nticuli interendotheliales) (Berens v. Rautenfeld, et al., 1976; Berens v. Rautenfeld, et al., 1983a; Berens v. Rautenfeld, et al., 1987a; and Berens v. Rautenfeld, et al., 1987b). Three transformation types of interendothelial openings exist (Berens v. Rautenfeld and Castenholz, 1987).

(4) Vas Iymphaticum precolligens [Vas I. precollectorium]; Vas lymphaticum iIbrotypicum; Trabecula fibroendothelialis. Precollectors (Fig. 13.1) form the first·

postsinusoidal section of the lymphatics equipped with valves and still situated within the organs (Berens v. Rautenfeld and Wenzel-Hora, 1985). Vas lymphaticum tibrotypicum (Nomina Histologica, 1989) has a subendothelial mantle of connective tissue fibres, but only occasionally has any smooth muscle cells (Berens v. Rautenfeld, et al., 1987a). Characteristic structural elements of the precollectors are connective tissue trabeculae (1:~beculae fibroendotheliales) (see Annot. 6) (Berens v. Rautenfeld, et al. 1983a; Berens v. Rautenfeld, et al. 1987a).

(5) Vas lymphaticum colligens [Vas I. collectorium]; Vas lymphaticum myotypicum; Vas lymphaticum colligens superticiale; Vas lymphaticum colligens profundum. All lymphatics vessels leading a~JrQ!!LJ!t.e organs (Fig. 13.1) are called "collectors" (Vas I. collectorium) (Berens v. Rautenfeld, et al., 1987a). Collectors are Vasa lymphatica myotypica (Fig. 13.3), Le., the media of these vessels possesses several layers of nonstriated muscle (Berens v. Rautenfeld, et al., 1984). Only short segments of ~ifascial collectors (Vasa lymphatica colligentia superficialia) exist in avian skin (Berens v. Rautenfeld, et al., 1983b). In the limbs, subfascial collectors "(Vasa Iymphatica colligentia profunda) form the main lymphovascular roiiie for lymph travelling centrally (Fig. 13.1).

(6) Cor lympbaticum; Trabecula myoiIbroendotbelialis. Lymph hearts may be present only embryonally, e.g., in Gallus (Romanoff, 1960), but also postembryonally in certain ratites, Anserinae, and Laridae (Baum, 1930). Budras and Berens v. Rautenfeld (1982), Budras and Berens v. Rautenfeld (1984), and Budras, et al. (1987)

deal with the functional and topographical anatomy of the lymph hearts in different birds. Lymph hearts remove lymph from the Phallus protrudens (Masc. Annot. 40). Lymph from the lymph hearts drains into the internal vertebral venous sinus (a Iymphovenous connection) Ven. Annot. 46, 82) (Budras and Berens v. Rautenfeld, 1984). Like collectors, lymph hearts have subendothelial smooth muscle cells, and a possibly unique type of striated muscle cell (Berens v. Rautenfeld and Budras, 1981; Budras and Berens v. Rautenfeld, 1983; Budras, et al., 1987). Their muscle connectivetissue trabeculae (Trabeculae myofibroendotheliales) contain striated muscle cells.

(7) Lymphonodulus solitarius [Nodulus lymphaticus solitarius); Centrum germinale. Solitary lymph nodules occur in most organs and tissues of the chicken.

"Mural lymphoreticular formations" (in the wall of the lymphatics) can be distinguished from parenchymal lympho~ticul~.JQ!:m~tions (in the parenchymas), and

tonsils (see Annot. 10). Solitary lymphoid nodules do not appear to be structurally comparable with the mammalian primary or secondary n~ules of the ,":0mfna HisTologica (NH) (1989). Avian nodules consist of thymus-derived lymphoid tissue, and often include bursa-derived avian germinal centres. Numerous synonyms eXIst (cf. Payne, 1971, and Rose, 1981). Avian germinal centres have a characteristic covering network of retJc~ar ce~s

(Olah and Glick, 1979), as well as blood capillanes; postcapillary venules WIth recirculating lymphocytes are always found outside avian germinal centers close to the reticular cells (Berens v. Rautenfeld and Budras, 1980; Berens v. Rautenfeld and Budras, 1983). The antigen-dependent formation of avian

(8) Lympbonodus [Nodus lymphaticus]; Vas lymphaticum afferens; Capsula; Sinus lymphaticus intranodalis; Cborda lymphoreticularis; Venula postcapillaris; Vas lympbhaticum efferens. Avian lymph nodes occur as cervicothoracic and lumbar lymph nodes in Anseriformes and certain other birds (Jolly, 1909-,1910; Fürther 1913) but not in Gallus (Baum, 1930). For reviews see Lindner (1961) and Rose (1981). Avian lymph nodes consist of a subordinate system of lymph sinuses,

Iymphoreticular cords and a thin capsule (Fig. 13.3) (Berens v. Rautenfeld, et al.,1981; Berens v. Rautenfeld and Budras, 1983; Berens v. Rautenfeld, et al., 1983a;

Berens v. Rautenfeld, 1985), and lack trabeculae and an uniform hilum (Lindner,1961; Berens v. Rautenfeld and Budras, 1983). The system of lymph sinuses cannot

be subdivided into special sections (e.g., marginal sinuses). The afferent and efferent lymphatics reaching far into the parenchyma of the node display valves (Fig. 1.3.~and a smooth muscle media (Berens v. Rautenfeld and Budras, 1983), and may muruc·the presence of a central lymph sinus (Rose, 1981). The lymphOl:eticular cords display B- and T-Iymphocyte areas (Sugimura, et al., 1977), postcapillary venules with recirculating lymphocytes, and a pool of free rnacrophages (Berens v. Rautenfeld and Budras, 1983). In anatids involution often begins even before sexual maturity (Berens v. Rautenfeld and Budras, 1983).

(9) Formatio lymphoreticularis muralis intema; Formatio lymphoreticularis muralis enema. Synonymy: Lymphonodulus muralis, NAA (1979); Sinus Iymphaticus intramuralis; Venula postcapillaris. Mural Iymphoreticular formations have been demonstrated in the wall of the lymphatics of many avian species (Kondo, 1937a; Kondo, 1937b; Biggs, 1957) including all examined (Berens v. Rautenfeld, et al., 1983b). For reviews Payne (1971) and Rose (1981). The new term "Formatio" was chosen because "lymphonodulus" (NAA, 1979) is a general term describing the structure of the secondary lymphatic tissue and is already in use. Mural formations also occur in ~es (Kampme~er, 196?). In the bird a distinction must be made between internal ana extex:naL....vanants (FIg. 13.4), Le., in the intima and externa of the lymphatics(Berens·v. Rautenfeld. et al., 1983a; Berens v. Rautenfeld, 1985). Only the external mural lymphoreticular formations have lymph sinuses (Fig. 13.4), which are coDDeaed to the lumen of the lymphatic vessel (Berens v. Rautenfeld et al., 1981; Berens v. Rautenfeld. et al., 1983b). Internal formations also occur in the wall of lymph hearts (Berens v. Rautenfeld, et al., 1981). According to Berens v. Rautenfeld (1985), murallymphoreticular for mations are avian lymph nodes which have developed postembryonally, since their I induction is antigen-<iependent. Mural formations can diSpiayau the structural features"/--of the 'f~,~nc!B-lymphocyte areas of nodes (McCorkle, et aI., 1979), postcapillar venules with recircula~.!>'mphocytes, and lymph sinuses (Berens v. Rautenfuld, 1985).

(10) Formatio Iymphoreticularis parenchymatosa. Parenchymal Iymphoreticular formations have been described in the literature as "ectopic lymphoid areas, lymphatic nodes, lymphoid follicles, focal lymphoid areas, secondary nodules, nodular lymphatic tissue" etc. (Payne, 1971). They are not listed in NAA (1979), but are categorised as "aggregated nodules". See Annot. 9 for the choice of the term "Formatio"; this term covers the general collections of lymphoid tissue scattered throughout the body (Rose, 1981). It includes secondary lymphoid tissue in the oculonasal region, liver, gall bladder, peripheral nerves, and skin (Rose, 1981), endocrine glands (Payne and Breneman, 1952; Cogburn and Glick,-1981), but not the lymphoid tissue proper in the digestive tract (see below). Parenchymal formations display postcapillary venules with recirculating lymphocytes (cf., Cogburn and Glick, 1981). 

(11) Corpuscula thymica. Synonymy: Hassal's corpuscles. The characteristics of these corpuscles in the chicken have been reviewed by Hodges (1974: 217-221).

(12) Bursa cloacalis. Synonymy: Bursa Fabricii (see Cloaca Annot. 11-13). The bursa is an appendage organ of the proctodeum in most birds (e.g., Gallus), but a

mural organ in ratites (Berens v. Rautenfeld and Budras, 1982). For reviews of the structure and function of the bursa see Payne (1971) and gg.~~ (1981); for the ontogenesis of the bursa in ratites see Muller (1985), and for involution of the bursa in Gallus and ratites see Berens v. Rautenfeld and Budras (I_~~2).

(13) Tunica mucosa bursalis; Plica bursalis. The arrangement and number of folds in the mucosa of the cloacal bursa varies with the species. Primary, secondary and tertiary folds can be distinguished (Berens v. Rautenfeld and Budras, 1982).

(14) Lobulus bursalis; Pars lymphoepitheliaIis; Pars lymphoreticularis; Lamina epithelialis interlobaris. The term "folliculus" in the NAA (1979) has been replaced by the term "lobulus" (Fig. 13.5), because in the bursa of most of the avian species examined, the lobuli (Fig. 13.5) project into the lumen (e.g., in ratites) (Mathis, 1938; Berens v. Rautenfeld and Budras, 1982). The term "folliculus" is characterized by mesenchymal structures. The term Pars Iymphoepithelialis and Pars Iymphoreticularis replace "medulla" and "cortex", respectively (Fig. 13.5). The notion of a central cortex and a peripheral medulla in the bursa of birds with projecting lobuli is misleading. The Pars lymphoepitheliales is comparable with the foIIicle-assocl/!ted epithelium of other lymphoepithelial organs (Holbrook, et aI., 1974; Glick, et 3J.., f977). Lamina epithelialis interlobularis is the epithelium between the Partes Iymphoepitheliales of the bursal lobuli (Holbrook, et aI., 1974). The term Septum interfolIiculare (NAA 1979) is omitted since this structure cannot be related to the projecting lobuli. For a review of the literature on avian species displaying projecting lobuli or invaginated lobuli (e.g., Gallus) see Berens v. Rautenfeld and Budras (1982). The projecting Lobulus may be developmentally primitive, since it is demonstrable only in the embryo of the chicken (Holbrook, et aI., 1974) and duck (Anas) (Miirk, 1944).

(15) Vagina periarteriaIis Iymphatica. Synonymy: "Periarterial lymphatic sheath".

(16) Splen. Synonymy: Lien, Several new terms are introduced for Iymphoid tissue of the white pulp and the tenninal vasculature. These terms are; Vagina penellipsoidea, Vasa capillaria penicillaria, Vasa capillaria pre-ellipsoidea, Vasa capillaria ellipsoidea, Vasa capillaria terminalia. See Fukuta, et aI. (l969a, b), and Olah and Glick (1982) for a review of the literature.

(17) Splen

(17) Splen accessorius. One or more small accessory spleens may occur near the spleen, weighing from 4 to 45 mg in 69 of 144 chickens (Gallus) (Glick and Sato, 1964).

(18) Lymphonoduli pharyngea1es/esophagea1es/c~es. Synonymy: pharyngeal, esophageal, cecal tonsils. Lymphoid tissues occur m the 1anun? p~pna .and (or) submucosa of the alimentary tract from Pharynx to Cloaca. The Identification of Band T-dependent areas in the cecal tonsils are described by Hos~i and Mori (1973). The term "gut associated lymphoid tissue" {GALTI has been widely used: The tonsils are LymphonodulLaggreg!!ti of relatively constant occurren~e and relatively ~arge

. size. The existence of Lymphonoduli ~phageales, however, IS somewhat dubiOUS,

but were described by'Zietschmarm (19t1), Schauder (1923), and Kovacs (1928).

(19) Anuli [Annuli] lymphatici jejunales/ilea1es. Cranial and caudal bands of

lymphoid tissue have been recorded in both the jejunum and ileum of Anas

(Leibovitz, 1968), but not in Gallus.

(20) Vasa Iymphatica colligentia [collectoria] (see Annot. 5). Dransfield (1944.

1945) provided the'most'detalled account of the distribution of lymphatic vessels. in

Gallus, but without naming them; Baum (1930) and Kondo (l937a) named the major

vessels. Previously unnamed lymphatic vessels are named herein according to the

blood vessels which they follow or the organs from which they drain lymph; some

previously named vessels have been similarly renamed. Most lymphatic vessels consist

of two or more parallel trunks with frequent anastomoses between them (Dransfield,

1944; 1945). For a topographical summary see King (1975: 2010-13),

(21) Truncus thoracoabdominalis. Usually right and left trunks are present, with

frequent anastomoses connecting them; sometimes present is a single vessel which

may bifurcate near its tennination (Figs. 13.6, 13.7). In Gallus the trunk or trunks

always terminate in the Ve~:_~~~e craniales (Miyaki. ~d Y~uda, 1977). ThoracIc

and lumbar parts of the thoracoabdominal trunk are dlstmgulshed by Baum (1930).

Dransfield (1944, 1945) restricted the term thoracic duct to the lymphatics cranial to

the celiac lymphatic plexus, and did not name the caudal part.

(22) Vas lymphaticum celiacum. The celiac lymphatic vessel (Fig. 13.6) receives

tributaries from the thoracic esophagus, proventriculus, gizzard, duodenum, ileum,

ceca, spleen, pancreas, and liver (Dransfield, 1944, 1945).

(23) Vas lymphaticum mesentericum craniale. The cranial mesenteric lymphatic

vessel (Fig. 13.6) receives branches from the jejunum, ileum, ceca, testis, ovary, and

the cranial part of the oviduct (Dransfield, 1944, 1945).

(24) Vas lymphaticum mesentericum caudale (Fig. 13.7). The caudal mesenteric

vessel drains lymph from the rectum (Dransfield, 1944, 1945).

(25) Vas lymph~ticum jugulare. Lymph carried by the jugular lymphatic vessel

empties into the Vena jugularis (Fig. 13.6) near the junction of the latter w~th yena

subclavia (Dransfield, 1944, 1945), or into either the Truncus

(26) Vas lymphaticum subclavium. The subclavian lymphatic vessel unites Lith

the Vena subclavia near the junction of the latter with the Vena jugularis (Fig. 11-6)

(Dransfield, 1944, 1945), or with the Truncus thoracoabdominalis or Vas 1ymplaticum

jugulare (Miyaki and Yasuda, 1977).

(27) Vasa lymphatica thoracica interna. The interniU thoracic lymphatics accpmpany

the Vv. thoracicae internae (see Ven. Annot.47), receive drainage from the

superficial lymphatics of the lung (Fig. 13.6) and abdominal muscles, and join the

Vena cava cranialis close to its origin (Dransfield, 1944, 1945).

(28) Vas lymphaticum cardiacum commune. The common cardiac lymphatic is a

single vessel (Fig. 13.6) which empties into the right Vena cava cranialis close to its

termination at the right atrium, its tributaries being independent of the coronary

arteries and veins (Dransfield, 1944, 1945).

(29) Vas lymphaticum pulmonale commune. The tributaries of the common vessel

receive lymph from the deep pulmonary lymphatics and travel along the left and right

pulmonary veins (Dransfield, 1944, 1945). The common pulmonary lymphatic is a

single vessel which joins the left Vena cava cranialis close to, or with, the Truncus

thoracoabdominalis (Fig. 13.6).

(30) Vas lymphaticum proventriculare. The proventricular lymphatic follows

the cranial proventricular vein (see Ven. Annot. 12), and joins the left Vena cava

cranialis close to, or in common with, .the left Truncus thoracoabdominalis (Dransfield,

1944, 1945).