THE ALIMENTARY TRACT WITH ITS APPENDAGES, THE SPLEEN, AND THE
PERITONEUM.
THE ALIMENTARY TRACT, ETC.
LITERATURE.
THE MOUTH.
(Except the mucous membrane of the tongue, for which see organ of
taste.)
*Ducrotay de Blainville, H. M.*, Ostéographie ou description
iconographique comparée du squelette et du système dentaire des
cinq classes d’animaux vertébrés. Paris, 1841.
*Erdl*, Ueber den Bau der Zähne bei den Wirbelthieren, etc. München,
1841.
*Fixen, C.*, De linguae raninae structura. Dorpat, 1857.
*Heincke, F.*, Untersuchungen über die Zähne niederer Wirbelthiere.
Zeitsch. f. wiss. Zool. 1873. Vol. XXIII, p. 495.
*Hertwig, O.*, Ueber das Zahnsystem der Amphibien, etc. Suppl. to
Vol. XI, Arch. f. mik. Anat. 1874.
*Hoffmann, C. K.*, Bronn’s Thierbuch. Leipzig and Heidelberg,
1873–1878. Vol. VI, p. 379.
*Holl, M.*, Zur Anatomie der Mundhöhle von Rana temporaria. Wiener
Acad. Sitzungsb. 1887. Vol. XCV, Pt. III, p. 47.
*Hoyer*, Ueber die Epithelzellen der Froschzunge, sowie über den
Bau der Cylinder- und Flimmerepithelien und ihr Verhältniss
zum Bindegewebe. Arch. f. Anat. u. Physiol. 1858, p. 163; also
Deutsche Klinik, 1857.
*Langer, C.*, Ueber das Lymphgefässsystem des Frosches. Wiener Acad.
Sitzungsb. 1867. Vol. LV, Pt. I, pp. 614–621.
*Leydig*, Die Anuren Batrachier der deutschen Fauna. Bonn, 1877.
*Owen, R.*, Odontography. London, 1840–1845, p. 187.
*Reichel, P.*, Beiträge zur Morphologie der Mundhöhlendrüsen
der Wirbelthiere. Leipzig, 1882; also in Morph. Jahrb. 1882,
Vol. VIII, pp. 1–72.
*Santi Sirena*, Untersuchungen über den Bau und die Entwicklung der
Zähne bei den Amphibien und Reptilien. Verhandl. d. phys.-med.
Gesellsch. in Würzburg, 1872. Vol. II, new series, p. 125.
*Schöbl, J.*, Ueber divertikelbildende Capillaren in der
Rachenschleimhaut nackter Amphibien. Sitzungsb. d. k. b.
Gesellsch. d. Wiss. in Prag. 1878, p. 25; also in Arch. f. mik.
Anat. 1885, Vol. XXV, p. 89.
*Schultze, F. E.*, Das Drüsenepithel der schlauchförmigen Drüsen des
Dünn- und Dickdarms und die Becherzellen (of the pharyngo-oral
cavity). Centralbl. f. d. med. Wiss. 1866, p. 61.
*Schultze, F. E.*, Epithel- und Drüsen-Zellen. Arch. f. mik. Anat.
1867. Vol. III, p. 137.
*Smith, W. J.*, Beitrag zur differentiellen Diagnose der Rana fusca
s. platyrrhinus und Rana arvalis s. oxyrrhinus auf Grund der an
den Gaumenzähnen nachweisbaren Unterschiede. Pflüger’s Arch. f. d.
ges. Physiol. 1883. Vol. XXXII, pp. 581–588.
*Tomes, C. S.*, On the development of the teeth of the newt, frog,
slowworm, and green lizard. Phil. Trans. 1874, p. 285.
*Török*, Untersuchungen über die Entwickelung der Mundhöhle, etc.
Wiener Sitzungsb. 1866. Vol. LIV, Pt. I, p. 75.
*Waller, A.*, Microscopic examination of the principal tissues of the
tongue, etc. Phil. Mag. 1846, pp. 273–290.
*Waller, A.*, On the development of the mouth and tongue of the frog.
Phil. Mag. 1850. Vol. I, pp. 38–43.
*Zeller, A.*, Die Abscheidung des indig.-schwefelsauren Natrons
in den Drüsen (Intermaxillary gland). Virchow’s Arch. 1878.
Vol. LXXIII, p. 257.
THE OESOPHAGUS AND STOMACH.
*Biedermann*, Untersuchungen über Magenepithel. Wiener Acad.
Sitzungsb. 1875. Vol. LXXI, Pt. III, p. 377.
*Bischoff*, Ueber den Bau der Magenschleimhaut. Arch. f. Anat. u.
Physiol. 1838, p. 503.
*Bleyer, E.*, Magenepithel und Magendrüsen der Batrachier. Dissert.
Königsberg, 1874.
*Braun*, Zum Vorkommen von Flimmerepithel im Magen. Zool. Anzeiger.
1880. No. 69, p. 568.
*Brinton*, in Cyclopaedia of Anat. and Physiol., edited by R. B.
Todd. 1859. Vol. I, p. 320.
*Cobelli*, Le gliandole acinose del cardia. Wiener Acad. Sitzungsb.
1866. Vol. LIII, Pt. I, p. 251.
*Ebstein, W.*, Beiträge zur Lehre vom Bau und den physiologischen
Funktionen der sogenannten Magenschleimdrüsen. Arch. f. mik. Anat.
1870. Vol. VI, p. 515.
*Ecker, A.*, Ueber die Drüsen der Magenschleimhaut. Zeitsch. f. rat.
Med. 1852, p. 243.
*Foster, M.*, On some points in the epithelium of the frog’s throat.
Journ. of Anat. and Physiol. 1869. Vol. IV, p. 394.
*Frerichs*, On the Stomach, in Wagner’s Handwörterbuch d. Physiol.
1848. Vol. II, p. 748.
*Glinsky, A.*, Zur Kenntniss des Baues der Magenschleimhaut der
Wirbelthiere. Centralbl. f. d. med. Wiss. 1883, p. 225.
*Gonjaew, K.*, Die Nerven des Nahrungsschlauches. Arch. f. mik. Anat.
1875. Vol. XI, pp. 479–496.
*Hebold, O.*, Ein Beitrag zur Lehre von der Sekretion und
Regeneration der Schleimzellen. Dissert. Bonn, 1879, pp. 21–27.
*Heidenhain, R.*, Untersuchungen über den Bau der Labdrüsen. Arch. f.
mik. Anat. 1870. Vol. VI, p. 368.
*Hoffmann, C. K.*, Bronn’s Klassen und Ordnungen des Thierreichs.
Leipzig und Heidelberg. 1873–1878. Vol. VI, pp. 408–412.
*Just, A.*, Zur Histologie und Physiologie des Flimmerepithels.
Breslauer ärztliche Zeitsch. 1885. No. 18, pp. 205–206.
*Klein, E.*, Darmkanal, in Stricker’s Gewebelehre, p. 388, etc.
*v. Kölliker, A.*, Mikroskopische Anatomie, 1854. Vol. II, p. 147.
*Langley, J. N.*, and *Sewall, H.*, On the changes in pepsin-forming
glands during secretion. Journ. of Physiol. 1880. Vol. II,
pp. 261, 281.
*Langley, J. N.*, On the histology and physiology of pepsin-forming
glands. Phil. Trans. 1881. Vol. CLXXII, Pt. III, pp. 663–712.
*Langley, J. N.*, On the structure of secretory cells and on changes
which take place in them during secretion. Internat. Monatschr. f.
Anat. u. Histol. Vol. I, pp. 69–76.
*Leydig*, Lehrbuch der Histologie. 1857.
*Nussbaum, M.*, Ueber den Bau und die Thätigkeit der Drüsen. Arch.
f. mik. Anat. 1882, Vol. XXI, p. 296; 1882, Vol. XXVIII, p. 296;
1877, Vol. XIII, p. 721.
*Partsch, C.*, Beiträge zur Kenntniss des Vorderdarmes einiger
Amphibien und Reptilien. Arch. f. mik. Anat. 1877. Vol. XIV,
p. 179.
*Regéczy, E. N.*, Ueber die Epithelzellen des Magens. Arch. f. mik.
Anat. 1880. Vol. XVIII, pp. 408–411.
*Robinson, C.*, Ueber die Lymphgefässe der Abdominaleingeweide des
Frosches, etc. Froriep’s Notizen, 1846. No. 807, col. 225.
*Rollett*, Bemerkungen zur Kenntniss der Labdrüsen und der
Magenschleimhaut. Untersuch. in d. Institut f. Physiol. u. Histol.
zu Graz. 1871.
*Schultze, F. E.*, Epithel- und Drüsenzellen. Arch. f. mik. Anat.
1867. Vol. III, p. 174; abstract in Centralbl. f. med. Wiss. 1866,
No. 4.
*Schmidt, C.*, Ueber eingenthümliche aus dem Flimmerepithel
hervorgehende Gebilde. Arch. mik. Anat. 1881. Vol. XX, p. 123.
*Sewall, H.*, A note on the processes concerned in the secretion
of the pepsin-forming glands of the frog. Studies in the Biol.
Laborat., Johns Hopkins Univers. Vol. II, pp. 131–134.
*v. Swiecicki, H.*, Untersuchungen über die Bildung und Ausscheidung
des Pepsins bei den Batrachiern. Pflüger’s Arch. f. d. ges.
Physiol. 1876. Vol. XIII, p. 444.
*Trinkler, N.*, Zur Kenntniss des feineren Baues der
Magenschleimhaut, insbesondere der Magendrüsen. Centralbl. f. med.
Wiss. 1883, pp. 161–163.
*Trinkler, N.*, Ueber den Bau der Magenschleimhaut. Arch. f. mik.
Anat. 1885. Vol. XXIV, p. 74.
*Trütschel*, Ueber die Endigung der Nerven in der Schleimhaut des
Magens. Centralbl. f. d. med. Wiss. 1870, p. 115.
*Valatour*, Recherches sur les glandes gastriques et sur les tuniques
musculaires du tube digestif dans les poissons ossieux et les
Batraciens. Annales de Sc. nat. 1861. Series IV. Vol. XVI, p. 219.
THE INTESTINE.
*Arnstein, C.*, Ueber Becherzellen, etc. Virchow’s Arch. 1867.
Vol. XXXIX, p. 527.
*Arnstein, C.*, and *Gonjaew, K.*, Ueber die Nerven des
Verdauungskanals. Pflüger’s Arch. f. d. ges. Physiol. 1874.
Vol. VIII, pp. 614–615.
*Auerbach, L.*, Fernere vorläufige Mittheilung über den Nervenapparat
des Darmes. Virchow’s Arch. 1864. Vol. XXX, p. 457.
*Auerbach, L.*, Untersuchungen über Lymph- und Blutgefässe. Virchow’s
Arch. 1865. Vol. XXXIII, p. 340.
*Auerbach, L.*, Organologische Studien.
*Billroth, T.*, Ueber die Epithelzellen der Froschzunge; der Bau,
Cylinder- und Flimmerepithel und ihr Verhältniss zum Bindegewebe.
Arch. f. Anat. u. Physiol. 1858, p. 159.
*Billroth, T.*, Einige Beobachtungen über das ausgedehnte Vorkommen
von Nervenanastomosen im Tractus intestinalis. Arch. f. Anat. u.
Physiol. 1858, p. 148.
*Brettauer* und *Steinach*, Untersuchungen über das
Cylinderepithelium. Wiener Akad. Sitzungsb. 1857. Vol. XXIII,
p. 303. Moleschott’s Zeitsch. 1857. Vol. III, p. 157.
*Darsch, O.*, Beiträge zur Kenntniss des feineren Baues des
Dünndarms. Wiener Sitzungsb. 1880. Vol. LXXXII, Pt. III, p. 168.
*Dönitz*, Ueber die Schleimhaut des Darmcanals. Arch. f. Anat. u.
Physiol. 1864, p. 367.
*Dönitz*, Ueber Darmzotten. Arch. f. Anat. u. Physiol. 1866, p. 757.
*Eberth, C. J.*, Ueber den feineren Bau der Darmschleimhaut. Würzb.
naturw. Zeitschr. 1864. Vol. V, p. 23.
*Eimer, T.*, Zur Fettresorption, etc. Virchow’s Arch. 1867.
Vol. XXXVIII, p. 428.
*Eimer, T.*, Ueber Becherzellen. Virchow’s Arch. 1868. Vol. XLII,
p. 490.
*Eimer, T.*, Zur Geschichte der Becherzellen. Dissert. 1867.
*Eimer, T.*, Die Wege des Fettes in der Darmschleimhaut bei seiner
Resorption. Virchow’s Arch. 1869. Vol. XLVIII, p. 119.
*Eimer, T.*, Zur Becherfrage. Virchow’s Arch. 1867. Vol. XL, p. 282.
*Erdmann*, Die Resorptionswege in der Schleimhaut des Dünndarms.
Dissert. Dorpat, 1867.
*Fries, E.*, Ueber die Fettresorption und die Entstehung der
Becherzellen. Virchow’s Arch. 1867. Vol. XL, p. 519.
*Gerlach, L.*, Ueber den Auerbachschen Plexus mysentericus. Arbeiten
aus d. physiol. Anstalt. Leipzig. 1872, pp. 102–112.
*Gonjaew, K.*, Die Nerven des Nahrungsschlauches. Arch. f. mik. Anat.
1875. Vol. XI, pp. 479–496.
*Gruby* and *Delafond*, Résultats des recherches faites sur
l’anatomie et les fonctions des villosités intestinales, etc.
Compt. rend. 1843. Vol. XVI, p. 1194.
*Grugenhagen, A.*, Ueber Fettresorption und Darmepithel. Arch. f.
mik. Anat. 1887. Vol. XXIX, p. 139.
*Heidenhain, R.*, Die Absorptionswege des Fettes. Moleschott’s
Untersuchungen. 1858. Vol. IV, p. 251.
*Henle, J.*, Symbolae ad anatomiam villorum intestinalium impr. eorum
epithelii et vasorum lacteorum. Berolini, 1837.
*Hoffmann, C. K.*, Bronn’s Klassen und Ordnungen des Thierreichs.
Leipzig und Heidelberg, 1873–1878. Vol. VI, pp. 412–424.
*Klein, E.*, Der Darmkanal in Stricker’s Gewebelehre, Article XVI.
*Klein, E.*, Contributions to the anatomy of Auerbach’s Plexus in the
intestine of the frog and toad. Quart. Journ. Micros. Sci. 1873.
Vol. XIII, p. 377.
*Klein, E.*, and *Verson, E.*, Der Darmcanal, in Stricker’s
Gewebelehre, 1871, p. 355.
*Klein, E.*, Der neue Nervenapparat v. Thanhoffer’s. Centralbl. f. d.
med. Wiss. 1883, p. 82.
*v. Kölliker, A.*, Nachweis eines besonderen Baues der Cylinderzellen
des Dünndarms. Verhandl. d. phys.-med. Gesells. Würzburg, 1856.
Vol. VI, p. 153.
*v. Kölliker, A.*, Handbuch der Gewebelehre.
*Lambl*, Ueber die Epithelialzellen der Dünndarmschleimhaut. Wiener
med. Wochenschr. 1859. Nos. 24 and 25.
*Langer, C.*, Ueber das Lymphgefässsystem des Frosches. Wiener Acad.
Sitzungsb. 1866. Vol. LIII, Pt. I, p. 395.
*Letzerich, L.*, Ueber die Resorption der verdauten Nährstoffe im
Dünndarm. Virchow’s Archiv. 1866, Vol. XXXVII, p. 232; 1867,
Vol. XXXIX, p. 435.
*Lipsky, A.*, Beitrag zur Kenntniss des feineren Baues des
Darmcanals. Wiener Akad. Sitzungsb. 1865. Vol. LV, Pt. I, p. 183.
*Oeffinger*, Einige Bemerkungen über die sogenannten Becherzellen.
Arch. f. Anat. u. Physiol. 1867, p. 337.
*Partsch, C.*, Beiträge zur Kenntniss des Vorderdarmes einiger
Amphibien und Reptilien. Arch. f. mik. Anat. 1877. Vol. XIV,
p. 179.
*Remak, R.*, Ueber peripherische Ganglien an den Nerven des
Nahrungsrohrs. Arch. f. Anat. u. Physiol. 1858, p. 189; also in
Zeit. d. Vereins f. Heilkunde in Preussen. 1840.
*Renzoni*, Osservazioni e ricerche sul epitelio intestinale.
Rendiconti dell Acad. di Napoli. 1868.
*Rusconi*, Riflessioni sopra il sistema linfatico dei rettili. Pavia,
1845.
*Sachs, J.*, Zur Kenntniss der sogenannten Vacuolen oder Becherzellen
im Dünndarm. Virchow’s Arch. 1867. Vol. XXXIX, p. 493.
*Schultze, F. E.*, Das Drüsenepithel der schlauchförmigen Drüsen des
Dünn- und Dickdarms und die Becherzellen. Centralbl. f. d. med.
Wiss. 1866, p. 160.
*Schultze, F. E.*, Epithel- und Drüsen-Zellen. Arch. f. mik. Anat.
1867. Vol. III, p. 145.
*Thanhoffer, L.*, Beiträge zur Fettresorption und histologischen
Structur der Dünndarmzotten. Pflüger’s Arch. f. d. ges. Physiol.
1874. Vol. VIII, pp. 391–443.
*v. Thanhoffer, L.*, Ein neuer Nervenapparat im Dünndarm. Centralbl.
f. d. med. Wiss. 1883, p. 33.
*v. Thanhoffer, L.*, Antwort auf Herrn Prof. Klein’s ‘Der neue
Nervenapparat etc.,’ betitelte Bemerkungen. Centralbl. f. d. med.
Wiss. 1883, p. 176.
*Valatour, M. M.*, Recherches sur les glandes gastriques et sur les
tuniques musculaires du tube digestif dans les poissons et les
Batraciens. Annales des Sci. nat. 4th Series, Vol. XVI. Zool.
1861, pp. 219–285.
*Watney, H.*, The minute anatomy of the alimentary canal. Phil.
Trans. 1877. Vol. CLXVI, Pt. II, p. 451.
*Wiegandt*, Untersuchungen über das Dünndarmepithel. Dissert. Dorpat,
1860.
*v. Wittich*, Beiträge zur Frage über Fettresorption. Virchow’s Arch.
1857. Vol. XI, p. 37.
THE LIVER, GALL-BLADDER, AND PANCREAS.
*Barfurth, D.*, Vergleichend-histochemische Untersuchungen über das
Glycogen. Arch. f. mik. Anat. 1885. Vol. XXV, p. 369.
*Brotz, J.*, and *Wagenmann, C. A.*, De amphibiorum hepate et
glandularum ductu excretio carentium structura deque earundem
functionibus experimenta. Berolini, 1841.
*v. Brunn, A.*, Flimmerepithel in den Gallengängen des Frosches.
Zool. Anzeiger. 1883. No. 148, p. 483.
*Eberth, C. J.*, Die Pigmentleber der Frösche und die Melanämie.
Virchow’s Arch. 1867. Vol. XL, p. 305.
*Eberth, C. J.*, Zur Kenntniss der Verbreitung glatter Muskeln.
Zeitschr. f. wiss. Zool. 1863. Vol. XII, p. 360.
*Eberth, C. J.*, Ueber den feineren Bau der Leber. Centralbl. f. d.
med. Wiss. 1866, p. 897.
*Eberth, C. J.*, Untersuchungen über die Leber der Wirbelthiere.
Arch. f. mik. Anat. 1867. Vol. III, p. 423.
*Eberth, C. J.*, Untersuchungen über die normale und pathologische
Leber. Virchow’s Arch. 1867. Vol. XXXIX, p. 70.
*Eberth, C. J.*, Ueber die Pigmentleber der Frösche. Virchow’s Arch.
1862. Vol. XXIX, p. 70.
*Gerlach, L.*, Ueber die Nerven der Gallenblase. Centralbl. f. d.
med. Wiss. 1873, p. 562.
*Hering, E.*, Ueber den Bau der Wirbelthierleber. Wiener Acad.
Sitzungsb. 1886. Vol. LIV, Pt. I, p. 335.
*Hering, E.*, Ueber den Bau der Wirbelthierleber. Arch. f. mik. Anat.
1867. Vol. III, p. 88.
*Hering, E.*, On the liver. Stricker’s Gewebelehre. 1872, p. 429.
*Hoffmann, C. K.*, Bronn’s Klassen und Ordnungen des Thierreichs.
Leipzig und Heidelberg, 1873–1878. Vol. VI, p. 424.
*Jones, C. H.*, On the structure and development of the liver. Phil.
Trans. 1849. Pt. I, p. 122.
*Langley, J. N.*, On variations in the amount and distribution of fat
in the liver-cells of the frog. Proc. Roy. Soc. 1886. Vol. XXXIX,
p. 234.
*Leydig, F.*, Lehrbuch der Histologie. 1857.
*Leydig, F.*, Die Leber der Fische und Batrachier.
*Nussbaum, M.*, Ueber den Bau und die Thätigkeit der Drüsen
(Pancreas). Arch. f. mik. Anat. 1877. Vol. XIII, p. 752.
*Popoff, M.*, The nerves of the gall-bladder (in Russian). Rudneff’s
Journ. f. normal. u. pathol. Histol., etc. 1872.
*Remak, R.*, Ueber runde Blutgerinnsel und über pigmenthaltige
Zellen. Arch. f. Anat. u. Physiol. 1852, p. 115.
*Weber, E. H.*, Ueber die periodische Farbenänderung welche die Leber
der Hühner und Frösche erleidet. Bericht von Verhandl. K. Säch
Gesell. Leipzig, 1850, p. 15.
*Zeller, A.*, Die Abscheidung des indig.-schwefelsauren Natrons in
den Drüsen (Pancreas). Virchow’s Arch. 1878. Vol. LXXIII, p. 257.
THE SPLEEN.
*Billroth, T.*, Beiträge zur vergleichenden Anatomie der Milz. Arch.
f. Anat. u. Physiol. 1857, p. 88.
*Billroth, T.*, Beiträge zur vergleichenden Anatomie der Milz.
Virchow’s Arch. 1861, Vol. XX, p. 410, and 1862, Vol. XXIII,
p. 457; also Zeitschr. f. wiss. Zool. 1862, Vol. XI, p. 325.
*Ecker*, Blutgefässdrüsen, in Wagner’s Handwörterbuch der
Physiologie. 1849. Vol. IV.
*Gray, H.*, On the structure and use of the spleen. London, 1854.
*Hoffmann, C. K.*, Bronn’s Thierbuch. Leipzig und Heidelberg,
1873–1878. Vol. VI, p. 509.
*v. Kölliker, A.*, Ueber den Bau und die Verrichtungen der Milz.
Mittheil. d. naturf. Gesell. in Zürich, 1847. Vol. I, p. 120.
*Kusnezoff, F.*, Ueber blutkörperchenhaltige Zellen der Milz. Wiener
Sitzungsber. 1873. Vol. LXVII, Pt. III, pp. 58–67.
*Müller, W.*, Ueber den feineren Bau der Milz. Leipzig und
Heidelberg, 1865.
*Remak, R.*, Ueber runde Blutgerinnsel und über pigmenthaltige
Zellen. Arch. f. Anat. u. Physiol. 1852, p. 115.
*Schweigger-Seidel, F.*, Untersuchungen über die Milz. Virchow’s
Arch. 1862. Vol. XXIII, p. 526.
*Stieda, L.*, Zur Histologie der Milz. Dorpat, 1862.
THE PERITONEUM.
*Alltmann, R.*, Ueber die Veränderungen des serösen Epithels am
blosgelegten Froschmesenterium. Arch. f. mik. Anat. 1878.
Vol. XVI, p. 111.
*Arnold, J.*, Ueber die Durchtrittsstellen der Wanderzellen durch
entzündete seröse Häute. Virchow’s Arch. 1878. Vol. LXXIV, p. 245.
*Batelli, A.*, Dello addaltamento di alcune cellule endotiali nelle
membrane serose. Lo Sperimentale. 1884, p. 132.
*Cyon*, Ueber die Nerven des Peritoneum. Bericht über d. Verhandl.
d. Kön. Säch. Gesell. d. Wiss. z. Leipzig, 1868. Vol. XX, p. 119.
Leipzig, 1869.
*Grunau, H.*, Ueber das Flimmerepithel auf dem Bauchfell des
weiblichen Frosches und über den Eileiterbau desselben. Dissert.
Königsberg, 1875.
*Hoffmann, C. K.*, Bronn’s Klassen und Ordnungen des Thierreichs.
Leipzig und Heidelberg, 1873–1878. Vol. VI.
*Hoffmann, T.*, Die Lungen-Lymphgefässe der Rana temporaria. Dissert.
Dorpat, 1875.
*Kapff*, Untersuchungen über das Ovarium und dessen Beziehungen zum
Peritoneum. Arch. f. Anat. u. Physiol. 1872, p. 553.
*Klein, E.*, On Remak’s ciliated vesicles and corneous filaments of
the peritoneum of the frog. Quart. Journ. Mic. Sci. New Series,
1872. Vol. XII, p. 43.
*Klein, E.*, On the peripheral distribution of non-medullated
nerve-fibres (nerves of the peritoneum). Quart. Journ. Micros.
Sci. 1872. Vol. XII, p. 32.
*Leydig*, Lehrbuch der Histologie. 1857, p. 325.
*Mayer*, Ueber die Flimmerbewegung. Froriep’s Notizen, 1836.
Vol. XLVII, p. 179.
*Neumann, E.*, Die Beziehungen des Flimmerepithels der Bauchhöhle zum
Eileiterepithel beim Frosch. Arch. f. mik. Anat. 1875. Vol. XI,
pp. 354–377.
*Nicolsky, P.*, Ueber das Flimmerepithel beim Frosche. Centralbl. f.
d. med. Wiss. 1880, p. 641.
*Paladino, G.*, Dell’ endotelio vibratile nei Mammiferi ed in
generale di alcuni dati sulla fisiologia delle formazioni
endoteliche. Estr. dal Giornale intern. delle Scienze Mediche.
1882. Vol. IV.
*Schweigger-Seidel* and *Dogiel*, Ueber die Peritonealhöhle der
Frösche. Arbeiten aus d. physiol. Anstalt zu Leipzig. 1866, p. 68.
*Solger, B.*, Ueber einige Entwicklungsstadien des Peritonealepithels
der Amphibien-larven. Manusc. d. Naturf. Versamml. zu Freiburg.
1884.
*Thiry*, Ueber das Vorkommen eines Flimmerepitheliums auf dem
Bauchfell des weiblichen Frosches. Göttinger Nachrichten. 1862,
pp. 171–174.
*Tourneux*, Recherches sur l’épithelium des sereuses. Journ. de
l’anat. et de la physiol. 1874.
*Waldeyer*, Eierstock und Ei. Leipzig, 1870, pp. 72 and 122.
*Wolff, W.*, Ueber freie sensible Nervenendigungen. Arch. f. mik.
Anat. 1882. Vol. XX, pp. 377–381.
THE ALIMENTARY TRACT, ETC.
I. THE ALIMENTARY TRACT.
The alimentary tract consists of the mouth or pharyngo-oral cavity, the
oesophagus, the stomach, the small intestine and the large intestine;
these together forming a tube extending from the mouth to the cloaca.
From the commencement of the oesophagus, at the entrance to the larynx,
to the end of the cloaca, the length of the tube is about 31.5 cm.,
that of the various parts being:
From glottis to pylorus 5.5 cm.
From pylorus to large intestine 22.0 cm.
Large intestine to end of cloaca 4.0 cm.
--------
Total length 31.5 cm.
========
A. The *Mouth*.
The mucous membrane covering the tongue will be described with the
sense-organs (see organ of taste).
*a.* *General description.* The mouth of _R. esculenta_, as in all
other amphibia, with the exception of the lowest (_Siren_, _Proteus_,
etc.), is of considerable width, and extends backwards as far as
the middle of the tympanic membrane. The upper margin of the mouth
possesses a lip or fold of the skin (_SS^{1}_), which projects
sufficiently to prevent the teeth being seen from the front or from
the sides. This lip-like rim is most prominent in the premaxillary and
superior maxillary regions, but can be traced along the whole length of
the upper jaw, and on to the lower jaw, by means of a well-marked fold
at the angle of the mouth. Beyond this point the lip is absent, as the
skin is closely attached to the bony mandible.
On the *roof* of the *mouth* the following structures can be made out:
immediately within the lip is a deep, well-marked groove, the outer
boundary formed by the lip, the inner by a fold of the mucous membrane
(Fig. 178 _F_); this fold increases from behind forwards as far as the
premaxillary bones, where it forms two prominences (_F^1_, _F^1_) with
an interval between. These correspond to the palatine processes of the
premaxillary bones: immediately behind them are openings of the ducts
of the intermaxillary glands. In the groove so formed are placed a
single row of simple teeth, which, though subject to many variations,
are usually about fifty in number.
[Illustration: Fig. 178.
The roof of the mouth.
_Cho_ Posterior naris.
_ID_ Opening of intermaxillary glands.
_F_ Fold of mucous membrane.
_F^1_, _F^1_ Prominences of mucous membrane.
_K_ Muscles.
_O_ Floor of the orbit.
_S_ Lip.
_S^1_ Lip.
_T_ Eustachian tubes.
_Vo_ Vomer.
]
A little further back and to either side of the median line is a small
group of vomerine teeth (_Vo_); each group has from five to ten teeth;
external to these is on each side a transversely-placed oval opening,
the posterior nares (_Cho_). These apertures are directed outwards and
backwards into a shallow groove, bounded anteriorly by a fold of mucous
membrane.
According to Wiedersheim the mucous membrane immediately around the
vomerine teeth is supplied with taste-bulbs; the epithelium surrounding
these being non-ciliated.
The roof of the mouth underneath the parasphenoid is somewhat vaulted
and on either side depressed by the eyeballs, which project downwards
more or less prominently (_O_, _O_). Still further back are the
openings of the Eustachian tubes (Fig. 178 _T_), one on each side, and
almost surrounded by the limbs of the pterygoid bones.
On the *floor* of the *mouth* (Fig. 179) the tongue (_Z_, _Z^1_)
forms the most prominent object; its shape varying according to the
state of contraction of its muscles. Behind it, in the middle line,
is a transverse groove (†), corresponding to the posterior border of
the hyoid bone, and still further back is the opening to the larynx
(_L_), a longitudinal slit about 3 mm. in length. The mucous membrane
to either side of the tongue is only slightly folded, and a little
in front of the angle of the mouth is depressed into an aperture
(_S_), opening into the vocal sac. This opening is surrounded by small
radiating folds of mucous membrane, and is oval in shape.
[Illustration: Fig. 179.
The floor of the mouth.
_K_ Muscles.
_L_ Opening to larynx.
_M_ Mandible.
_S_ Opening to voice-sac (in males only)
_Sm_ Chin.
_Z_ Tongue.
_Z^1_ Left cornu of bifid tongue.
† Folds opposite hinder border of the hyoid.
]
Towards the oesophagus the mucous membrane of both the roof and the
floor of the mouth is thrown into numerous longitudinal folds.
*b.* The *minute structure* of the several parts.
(1) The *mucous membrane* of the mouth. At the junction of the skin and
the mucous membrane there is a gradual transition from the stratified
epithelium of the skin to a single layer of *columnar epithelium*. On
the floor of the mouth this condition is reached at the tongue; on the
roof the transition takes place more quickly. The columnar epithelium
of the mouth (that of the tongue is excluded from this description) is
ciliated; scattered cells, which are not ciliated, are found here and
there irregularly, but are not numerous. The cylindrical cells are very
finely granular in their upper parts, clearer in the middle portion,
more coarsely and darkly granular in their deeper portions; each cell
is possessed of a large, well-defined, oval nucleus, which contains one
or sometimes two nucleoli. The non-ciliated cells usually present a
sharply differentiated, structureless, hyaline, free border (Schultze).
The epithelium towards the margin of the mouth, where it is stratified,
is also ciliated.
Goblet-cells occur in every part of the epithelium, whether ciliated or
non-ciliated, and their forms vary very greatly.
[The *submucous layer* is a fibrous connective-tissue matrix, very rich
in nerves and blood-vessels. The capillaries are arranged in small,
somewhat polygonal meshes (Fig. 180), and are peculiar, with those of
the anterior part of the oesophagus, in having small dilatations. This
arrangement was first[71] described by Langer, and later by Schöbl. The
dilatations are placed quite irregularly on the capillaries, sometimes
only on one side, sometimes on both sides of the vessel; a slight
constriction occurs at the neck of each dilatation, where it opens
into the capillary[72]. The nerves of the mucous membrane underneath
the orbits have nerve-cells attached to them (Stirling and Macdonald,
page 170). The lymphatics are very numerous, and for the most part
follow the course of the blood-vessels to their finest twigs, beyond
which they follow an independent course (Langer).]
[Footnote 71: Beale, Phil. Trans., 1863, p. 153, shows dilatations in
his drawing, but makes no reference to them in the text.]
[Footnote 72: The vascular supply of the mucous membrane of the dorsal
surface of the mouth and oesophagus is shown (after Schöbl) in Plate
II, Fig. 180, I. Arteries red, veins blue. II. in the same figure
represents the dilatations on the capillaries; after Schöbl.]
(2) The *teeth* are wanting in the lower jaw; on the roof of the mouth
they are found in two situations: as a single row in the groove within
the lip, and a group on each vomer. Each tooth has the form of an
elongated cone, which in the case of the jaw-teeth is curved, in that
of the vomerine teeth straight. The teeth are fixed to the jaw so as to
project upwards and slightly inwards, those at the front of the mouth
projecting backwards, and those on the vomers project backwards. Each
tooth has a small, sharp projection, or secondary crown on its outer
surface (Fig. 181), placed near the mucous membrane. The teeth are
fixed to the bones by means of _Crusta petrosa_, which is again united
to the bones of the mandible by a matrix of spongy bone, continuous
for the several teeth. Between the tooth and the mucous membrane is a
layer of flattened epithelium (_II_), which extends more deeply on the
inner side of the tooth than on the outer; the layer is continuous with
the epithelium of the mouth, and is two to three cells in thickness.
Each tooth has fine longitudinal grooves on the basal part of its
outer surface, and consists of two parts, a crown and a root. The
teeth possess large cavities, the wall being thin and almost of even
thickness, except on the inner surface of the basal portion of the
root, where the wall is wanting, and so forms a large aperture to the
root.
The general skeleton of the tooth is formed of dentine, this is covered
on the crown by a layer of enamel, and the _Cuticula dentis_ on the
socket by a layer of _Crusta petrosa_.
α. The *dentine* is a homogeneous substance pierced by numerous
tubules (_D_), which arise at the pulp-cavity and course in a parallel
direction to the surface of the dentine, where they form a rich
network with irregular, interglomerular spaces. The inner surface of
the dentine is rough, through the presence of numerous small, dark
tubercles.
β. The *enamel* covers the dentine on the apical portion of the tooth.
It has tubes coursing through it, which are continuous with those of
the dentine, and presents also circumferential striations (Fig. 181
III).
[Illustration: Fig. 181.
I. Transverse section of the premaxillary bone to show attachment of
the teeth; after Hertwig. Magnified 22 times.
II. Dentine and enamel; after Hertwig. Magnified 500 times.
III. Enamel: after Hertwig. Magnified 500 times.
_A_ Blood-vessel of the pulp-cavity.
_C_ Crusta petrosa.
_D_ Dentine.
_F_ Processus dentalis.
_H_ Layer of epithelium.
_O_ Tooth cuticle.
_R_ Reserve.
_S_ Enamel.
_X_ Cutaneous glands.
]
γ. The *tooth cuticle* (_Cuticula dentis_) is colourless and covers the
enamel. It is highly refractive, very transparent, and very resistant
to chemical reagents. From the apex, towards the _Crusta petrosa_,
it thins very rapidly, but is continued sufficiently far to cover a
portion of the _Crusta petrosa_.
δ. The _Crusta petrosa_ resembles bone, except that it contains no
Haversian canals; it possesses cells which resemble bone corpuscles,
and are usually somewhat rounded or oval and communicate with each
other by their processes; for the most part it is homogeneous and free
from cells (Hertwig).
ε. The *pulp-cavity* contains a connective-tissue very rich in cellular
elements; those cells adjacent to the dentine are arranged in a layer
(_Membrana eboris_) which has somewhat the appearance of a layer of
epithelium. The cells (odontoblasts) of this layer are spindle-shaped,
and send processes (dentinal fibres) into the dentinal tubules. A small
blood-vessel can be traced into each cavity, but as yet no nerve has
been found in the pulp-cavities.
[Smith (_l. c._) has, after careful investigation, come to the
conclusion that the teeth of _R. esculenta_ and _R. temporaria_ are
practically alike, therefore the methods of differentiating the two
species by means of the teeth, as given by Leydig, are not to be relied
on.]
(3) The *intermaxillary glands* (_Glandula intermaxillaris_) consist
of a mass of convoluted tubes, lying chiefly between the premaxillary
bones and the capsule of the nose, and opening by about twenty to
twenty-five ducts at the fore-part of the mouth (Fig. 178 _ID_). A
portion of the glands extends high into the nasal cavity (Born), while
dorsally another portion lies under the skin and the _M. dilatator_
and _M. lateralis narium_, which together act as compressors to the
subjacent glands: a small, elastic, cartilaginous rod, placed between
the anterior margin of the nasal capsule and the under surface of the
ascending limb of the premaxilla, opposes these muscles on either side
by its spring-like action (Wiedersheim).
In a fresh skull the openings of the ducts can easily be seen after
washing away the mucous secretion; they are, however, seen to better
advantage by treatment with Müller’s fluid and subsequent staining with
carmine. With sufficient magnifying power, they are then seen as a row
of bright dots. The tubules are of uniform thickness, placed closely
side by side, and surrounded by a nervous plexus, which contains
numerous branching nerve-cells. The epithelium of the tubules is
cylindrical, with a rounded, finely granular nucleus; processes from
the peripheral ends of the cells are continued to a _Membrana propria_.
The ducts are lined with columnar, ciliated epithelium.
The *secretion* of the glands is remarkably adhesive, and is wiped off
by the tongue when it is projected; by this means the tongue becomes a
particularly efficacious instrument for capturing prey. The glands are,
both histologically and chemically, pure mucous glands. In urodeles the
homologous glands are placed in the hollow septum of the nose, between
the nasal cavities.
(4) The *tongue* (Figs. 179, 182, 183) is a broad, fleshy flap on the
floor of the mouth, to which it is attached by the anterior half of its
ventral surface as far forwards as the chin. Seen from above it has a
wedge-like form, being narrow in front and wider behind, where it is
prolonged at each angle to form two cornua.
By raising the tongue one obtains a view of a portion of the _M.
hyoglossus_. The two _MM. hyoglossi_ arise (see page 66) some distance
apart, and run forwards and towards each other to meet on the ventral
surface of the hyoid bone; they now assume a longitudinal direction,
and course forwards parallel to each other until they reach the _M.
genio-glossus_ (Fig. 182 _G_). Each muscle now divides to form coarse
bundles, which ascend on either side of the _M. genio-glossus_ towards
the dorsum of the tongue. In this course they are encircled by a
strong, elastic, connective-tissue sheath. The sheath is incomplete at
the hinder end of the _M. genio-glossus_, where it possesses rounded
apertures, through which the glossopharyngeal nerves (_N_, _N_)
disappear, to be distributed, after a sharp curve backwards, in the
substance of the organ.
The _M. genio-glossus_ arises, in two parts on either side, at the side
of the chin. One part (Fig. 182 _G_) is dorsal and median, the other
(Fig. 182 _G^1_) ventral and external.
[Illustration: Fig. 182.
Muscles of the tongue, seen from the ventral surface.
_G_ Median portion of M. genio-glossus.
_G^1_ Lateral portion of M. genio-glossus.
_H_ Hyoid.
_Hy_ M. hyoglossus.
_L_ Larynx.
_M_ Mandible.
_N_ Glossopharyngeal nerve.
]
The first part, with its fellow of the opposite side, forms an arched
commissure in the form of muscular rings, which decrease in size
from before backwards, and so form a pear-shaped mass: the second,
external portion, extends backwards, with a slight obliquity, as a
thin, fan-like expansion, to the mucous membrane, where it is inserted.
This arrangement can easily be seen after dissecting away the sheath
(Fig. 183 _Hy_); the hindermost fibres curve sharply into the tongue
(_Hy^1_); the anterior fibres pass obliquely forwards and blend with
the straight fibres of the dorsal portion of the _M. genio-glossus_
(Fig. 183 _Gg_). The arcuate fibres of the _M. genio-glossus_ pass,
for the most part, upwards and outwards to the tips of the posterior
bifid border of the tongue; in this course they lie as a rule above the
_M. hyoglossus_, but here and there the two muscles intermix (Fig. 183
_Gg^1_), and it is by no means easy to separate them.
The _M. hyoglossus_ is the retractor of the tongue, the _M.
genio-glossus_ the protractor.
(For mucous membrane of the tongue, see organ of taste. The vocal sacs
are described with the organs of voice and respiration.)
B. The *Oesophagus* and *Stomach* (Figs. 184, 185, 189, 194, 195, 199).
*a.* *General description.* The oesophagus is not separated from the
pharyngo-oral cavity by a sharp line of demarcation. It has a length of
only a few mm. in medium-sized frogs (Fig. 184 _Oe_), and lies in the
middle line of the body, supported on either side by the cornua of the
hyoid bone. The oesophagus lies on the dorsal wall of the larynx, is
smooth externally, and is thrown into well-marked longitudinal folds
internally.
[Illustration: Fig. 183.
Muscles of the tongue, from the ventral surface.
_G_ M. genio-glossus.
_Gg_ Straight fibres of the M. genio-glossus.
_Gg^1_ Curved fibres of the M. genio-glossus.
_Hy_ and _Hy^1_ M. hyoglossus.
_Z_ Borders of the tongue.
]
The transition from oesophagus to stomach is somewhat indefinitely
marked by a slight dilatation of the tube, often scarcely perceptible,
still it can always be recognized by an abrupt curvature to the left
(Fig. 184 _M_), which becomes more prominent when the stomach is
distended. Externally the stomach is seen as an elongated, slightly
curved cone, smooth externally and of equal diameter throughout.
The oesophagus and stomach are held in position by folds of peritoneum
(mesentery), which attaches them to the dorsal wall of the abdominal
cavity, to the lungs, pericardium, and liver; and by the blood-vessels.
*b.* *Minute structure.* The walls of these viscera are composed of
four layers or coats.
(1) The *serous coat* (Fig. 186) is a layer of endothelium, lying on
a very thin stratum of connective-tissue; the whole derived from the
peritoneum, which encloses the organs.
(2) The *muscular coat* (Fig. 186 _LM_ and _TM_) is arranged in two
layers, one (_LM_) longitudinal, the other (_TM_) transverse. The
longitudinal layer is thicker in the oesophagus, and thins as it is
continued to the pyloric end of the stomach. The circular layer, on the
other hand, gains in thickness; both layers are of unstriated muscular
fibre.
[Illustration: Fig. 184.
The alimentary canal.
_A_ Opening of large intestine into cloaca.
_Cl_ Cloaca.
_D_ Small intestine.
_Du_ Duodenum.
_HB_ Urinary bladder.
_M_ Stomach.
_Mz_ Spleen.
_Oe_ Oesophagus.
_Py_ Pylorus.
_R_ Large intestine (rectum).
† Junction of small and large intestine.
]
(3) The *submucous coat* (Fig. 186 _A_, _B_, and _SM_) is better
developed in the stomach than in any other part of the alimentary
canal. It is formed of a wide-meshed, loose connective-tissue, which
supports numerous blood-vessels and lymphatics. Towards the mucous
coat it possesses a well-differentiated _Muscularis mucosa_, which is
arranged in two layers, a longitudinal (_B_) and a transverse (_A_).
(4) The *mucous coat* is possessed of numerous tubular glands, which
vary in structure according to the part of the membrane examined. They
have been the subject of much investigation (Heidenhain, Nussbaum,
Partsch, Langley, and others), and are best described in three groups:
those of the oesophagus, of the first part of the stomach, and of the
pyloric end of the stomach respectively; between each pair of groups
are transitional forms.
α. [The oesophageal glands are complete tubular glands lined by a
single layer of epithelium, which very closely resemble the glandular
cells of the fundus of the stomach (Plate II, Fig. 187). The cells
are conical or cylindrical, the protoplasmic contents granular, the
granules being larger than those of the corresponding cells in the
stomach (Langley). Mucous cells are found among the true secretory
cells. The cells of the ducts are sometimes, but rarely, ciliated
(Langley).]
[Illustration: Fig. 185.
The abdominal viscera of _Rana esculenta_ (female).
_D_ Small intestine.
_Du_ Duodenum.
_EE_ Ovaries.
_H_ Heart.
_HB_ Urinary bladder.
_L_ Left lobe of liver.
_L^1_ Right lobe of liver.
_L^2_ Middle lobe of liver.
_Lg_ Left lung.
_Lg^1_ Right lung.
_M_ Stomach.
]
β. [The glands of the fundus of the stomach[73] are not so complex as
the typical glands of the oesophagus. The cells at the mouth of the
gland are continued into fine processes (Fig. 187), and their outer
parts contain mucigen. The cells of the neck of the gland are more
cubical, and towards the lower part of the neck are mucous cells. The
cells of the body of the gland are of irregular shape, and so placed
that the nucleus of one cell faces the junction of two cells on the
opposite side (Langley). These cells are very finely granular.]
[Footnote 73: A transverse section through the mucous membrane of
the fundus of the stomach of _Rana esculenta_ is shown in Plate II,
Fig. 187. Alcohol preparation, doubly stained with carmine and anilin
blue. After Biedermann. (Obj. II, Syst. 7, Hartnack.)]
[Illustration: Fig. 186.
Transverse section through one of the longitudinal folds of stomach of
_Rana temporaria_. To show general arrangement of the walls.--G. H.
_A_ Transverse layer of muscularis mucosae.
_B_ Longitudinal layer of muscularis mucosae.
_LM_ Longitudinal muscular coat.
_M_ Mucous membrane.
_SM_ Submucous coat.
_TM_ Transverse muscular coat.
]
γ. [The glands of the pyloric end of the stomach have been compared
with the mouths and necks of the glands of the fundus (Partsch,
Langley). The cells are of two kinds only (Fig. 188). The cylindrical
cells of the surface of the stomach are continued into the gland, where
they become shorter and sub-cubical; these form the greater part of the
gland. The cells at the deepest portion of the gland are more rounded,
and resemble the mucous cells in the neck of the glands of the fundus.]
δ. [Between these well-marked groups of glands are various transitional
forms. The transition from oesophageal to gastric glands is not a
continuous one, as glands resembling those of the stomach can be found
nearer the oesophagus than other glands, which more nearly resemble
oesophageal glands. At the same point the mucous membrane is thinner
than either in front or behind. In the same way an intermediate zone
exists between the typical glands of the fundus and pylorus of the
stomach.]
In both oesophagus and stomach the mucous membrane is thrown into
longitudinal folds when the organs are empty. The epithelium of the
surface of the oesophagus is mostly ciliated, and possesses numerous
goblet-cells; according to Klein the cells are not set vertically on
the subjacent submucosa, but obliquely.
[The epithelium of the surface of the stomach is, at least in part,
ciliated (Regéczy, Trinkler, and others), and has numerous goblet-cells
(Schultze, Heidenhain, Bleyer, Eimer, Oedmonson, and others).]
[Illustration: Fig. 188.
Transverse section through the mucous membrane of the pyloric end of
the stomach of _Rana esculenta_. After Partsch. (Obj. II, Syst. 7,
Hartnack.) ]
(5) [The *nerves* of these organs, according to Gonjaew, contain both
medullated and non-medullated fibres, which have nerve-cells attached
to them. From these fine branches pass, either with the blood-vessels
or alone, to the mucous coat, losing their medulla on the way. In this
course they inosculate very freely, and are then distributed as very
fine, beaded fibrils to the glands and epithelium, which are very
richly supplied.]
(6) [The *blood-vessels* and *lymphatics* very closely resemble
the corresponding structures in the small intestine (p. 290); the
blood-vessels form a rich anastomosis in the submucous membrane; the
lymphatics are arranged in two systems, one under the serous coat, and
a larger system in the mucous and submucous coats. The oesophagus lies
free in a peri-oesophageal lymph-sac (Robinson).]
C. The *Small Intestine*.
*a. General description.* The small intestine commences behind the
middle of the abdomen at the pyloric end of the stomach, from which it
is marked off by a slight constriction. The first portion of the small
intestine is the duodenum (Figs. 184 and 194 _Du_); by means of an
abrupt turn it winds directly forwards, parallel to the long axis of
the stomach; the pancreas is placed in the loop so formed.
The whole of this portion of the intestine, together with the greater
part of the stomach, is, in the normal condition, under cover of the
liver (Figs. 185, 194): while under the liver the intestine is firmly
attached to the deep surface of that organ by a short but strong
_Ligamentum hepato-duodenale_; it then turns suddenly backwards,
increases in size, and by means of numerous convolutions occupies a
considerable portion of the right half of the abdomen (Fig. 184 _D_).
It is held in position by a well-developed mesentery.
*b.* *Minute structure.* Like other portions of the alimentary canal,
the small intestine is formed of four layers:--
(1) The *serous coat* presents no peculiarities; it consists simply of
a layer of endothelial cells, with a small amount of sub-endothelial
connective-tissue.
(2) The *muscular coat* is in two layers, the outer longitudinal layer
being very thin, the inner circular layer thick.
(3) The *submucous layer* resembles that of the stomach, but is not so
thick; the _muscularis mucosae_ is well developed and arranged, as in
the stomach, in two layers.
(4) The *mucous coat* (Fig. 189) is thrown into folds, which differ in
various parts of the tube.
The longitudinal folds of the stomach are compressed together towards
the pyloric end of the stomach (_a_) and diminish in size; at the
commencement of the duodenum they end abruptly (_a^1_), but without any
indication of a valvular arrangement.
Immediately beyond the pylorus the mucous membrane is folded so as to
form an irregular network of folds which inclose irregular alveoli;
the folds are thicker on the concave surface of the duodenum, and form
a longitudinal ridge (_b_); in this ridge the alveolar spaces are
much smaller than those to either side. The irregular folding extends
through two to three cm., when a more regular arrangement commences in
the form of two adjacent series of transverse folds (_c, c^1_). Each
fold is semi-lunar in shape, with the convexity attached to the wall
of the tube and directed forwards, while the concave free border and
pocket-like space enclosed are directed backwards.
The arrangement of these folds reminds one of the semi-lunar valves of
the human heart, and probably one of their functions is to prevent the
regurgitation of the chyme (Wiedersheim).
The corresponding valves of opposite sides meet at each end at an
angle, the apex of which is directed away from the stomach. On these
folds and between them are smaller, secondary folds, partly irregularly
arranged, partly longitudinal (_d d_).
Towards the middle of the small intestine this valvular arrangement
is lost, to be replaced by an irregular net-like folding; beyond this
longitudinal folds arise, which proceed in a sinuous course towards the
large intestine.
The whole mucous membrane, both on the folds and otherwise, is covered
with a simple layer of columnar epithelium, which is continued into
numerous simple follicles (glands of Lieberkühn) found throughout
the mucous membrane of the small intestine. The cells are placed
on a basement membrane, which rests on a thin layer of loose
connective-tissue, intervening between the epithelial coat and the
_muscularis mucosae_. The epithelial cells are intermixed with a large
number of goblet-cells, and have between them fine processes from the
connective-tissue corpuscles of the subjacent layer; many of these
processes extend to or even beyond the free margin of the epithelial
cells.
[Illustration: Fig. 189.
Mucous membrane of the pyloric end of the stomach and the duodenum.
_a_ Mucous membrane of the stomach.
_a^1_ Commencement of duodenum.
_b_ Duodenal mucous membrane arranged in irregular network.
_c_ } Semi-lunar folds of
_c^1_} the mucous membrane.
_d_ Longitudinal folds of the mucous membrane.
]
The individual cells are columnar, possessed of a well-marked
cell-wall, and have distinct, large, oval nuclei, containing one
or more nucleoli. The protoplasmic contents are granular, and with
proper treatment show a very distinct intracellular network. The free
margins of the cells are sharply marked off from the cell-contents,
and are more firmly attached to the corresponding portions of adjacent
cells than the rest of the cell-wall. This margin has a longitudinal
striation, which owing to the important function performed by this part
of the intestine, namely, absorption of the fat, has been the subject
of many important investigations.
[In the following brief summary of the earlier researches on
the minute structure of the intestinal epithelium, in which the
intestine of the frog was chiefly used, the memoirs in which these
investigations are recorded are referred to in the order of time.
1837. Henle first described the border as a thickened, highly
refractive portion of the cell-wall.
1855. Kölliker and Funke, after independent research, described the
longitudinal striation: Funke offered no explanation of the fact,
while Kölliker considered it due to the presence of fine tubules.
Later Funke gave a modified support to Kölliker’s view by admitting
the presence of tubules around the circumferential part of the border.
1856. Donders gave a description corresponding with that of Henle.
1857. Brettauer and Steinach gave it as the result of their
investigations that the border was composed of closely-applied fine
rods: v. Wittich first showed that the borders of adjacent cells
were more firmly attached than the rest of the cell; he admitted the
presence of apertures, but considered the whole appearance to be due
to post-mortem changes.
Welcker and Friedreich agreed with the views of Brettauer and
Steinach, but traced the striation throughout the length of the
cells, in fact traced the tubules to the connective-tissue below.
1858. In this year Heidenhain published his results; he held the
striation to be due to the presence of fine rods, and was the first
to show that processes of the connective-tissue corpuscles passed up
between the epithelial cells; he found fat globules in the epithelial
cells, in the connective-tissue, and in the lacteals.
Friedreich described the striation as continued through the whole
length of the cells, and as due to tubules.
1859. Lambl denied the presence of the rods, and considered the whole
phenomenon an optical appearance due to the cell-wall; in this view
he was supported by Vlakovich of Padua and Amici of Florence.
1860. Wiegandt held the border to be an independent covering, and the
striation to be due to folding or wrinkling.
Col. Balogh described the border as formed of rods, but denied that
these existed except when brought about by the action of fats; in
support of this view he showed that the striation was wanting when
fat was absent.
1865. Lipsky held the border to be composed of rods.
1866. Henle described the cells as in his former work, but now held
the border to be composed of rods, in fact to represent a ciliated
border.
1867. Erdmann described the border as being of two layers, an upper,
thicker layer, with both longitudinal and transverse striation,
and a lower, thinner layer, the true cell-wall. The upper layer
he described as capable of splitting in the directions of both
striations.
Schultze described the border as not being in intimate connection
with the protoplasm of the cell. Arnstein and Wiegandt supported
Heidenhain’s description.
1868. Albini e Renzoni described the part as resembling resting cilia.
1869. Eimer traced fat-globules into all the parts, epithelium,
connective-tissue, and vessels; and held that the fat could pass from
a lacteal to a branch of the Vena porta.
1870. Heidenhain, after further investigation, supported his earlier
views.
1874. Thanhoffer described the membrane as perforated, and the
protoplasm of the cells as actively sending protoplasmic processes
through these apertures; this he had seen in frogs in which all
connection with the spinal nerves had been severed.
1875. Benjamins could not find the striation to be a constant
occurrence, and failed to find the processes described by Thanhoffer.
1876. Krause found rod-like bodies round the margin of the border.
1877. Fortunatow supported Thanhoffer’s view.
1881. Landois observed appearances in Spelerpes fuscus, which led him
to support Thanhoffer’s views.
1883. Wiedersheim supported Thanhoffer’s views.
1884. Wiemer supported Thanhoffer’s observations.
1888. Paneth failed to find any contractile protoplasmic processes,
and asserts that the circumference of the border, when examined under
certain conditions, is composed of rods.
From the same causes the goblet- or chalice-cells, already mentioned,
have been the subject of much speculation and investigation.
1846. Frerichs drew and described these cells as empty cells.
In 1848 these cells were first described as epithelium capitatum by
Gruby and Delafond.
In 1856 Donders described the cells as being open, and as discharging
their contents into the canal; the cell-walls being then pressed
together by the neighbouring cells, and the cell-contents being then
gradually reformed.
In the same year Kölliker published results closely agreeing with
those of Donders, and he traced the various stages of the process.
1857. Brettauer and Steinach held them to be cells which had lost
their contents, and as the ‘cuticular border’ was absent, concluded
that the cell-contents were in closer connection with the ‘border’
than with the rest of the cell-wall.
1865. Lipsky and Sachs both doubted the presence of such cells, and
considered them due to the action of reagents or post-mortem change.
1866. Letzerich described the cells as open, and regarded them as the
commencement of the lacteal system, while Dönitz thought the whole
appearance due to reagents.
1867. Schultze and Eimer, independently, described them as
unicellular glands. Erdmann, however, again denied their occurrence
under normal conditions.
Oeffinger held the goblet-cells to be modified ordinary cylindrical
epithelium cells; in which view he was supported by Arnstein.
1868. Schultze and Eimer, after renewed investigations, reiterated
their former opinions.
1869. Eimer described the goblet-cells as secreting mucin, and as
capable, by division, of throwing out pus-like cells.
1876. Krause described the cells as containing granular contents,
which under certain conditions are thrown out.
1877. Tolldt considered them artificial productions. Edinger asserted
that they are formed from the cylindrical cells.
1877–1885. Partsch (1877), Klein and Hebold (1879), Stöhr (1880),
Patzelt (1882), Haller (1883), Holl (1885), support the last view.
1878. Hoffmann supported Schultze’s views.
1886. List describes these organs as unicellular mucous glands.
1887. Paneth described them as secreting mucous and as being derived
from the cylindrical cells.]
(5) [The *blood-vessels* of the small intestine (p. 234) have been
described by Langer; he finds the vessels arranged in networks, one
a subserous network, placed underneath the serous coat, and formed
of elongated, irregular, four-cornered meshes. When the intestine is
distended the meshes are rectangular.
The vessels to the mucous membrane divide and anastomose very freely
in the submucous layer, and then form an irregular network on the
inner surface of the _Muscularis mucosa_; this network follows all the
foldings of the mucous membrane, and thereby supplies a double layer
to each villous fold of the mucous membrane. The meshes are usually
four-sided or five-sided.]
(6) [The *lymphatics* of the small intestine (Figs. 190, 191). The
lymphatic vessels on reaching the intestine usually bifurcate; the two
branches, as a rule, follow and enclose an arterial twig. From the
serous layer they receive the contents of a very fine lymphatic plexus,
the lumens of which are slightly greater than that of the corresponding
capillaries; from the mucous layer they receive the contents of the
lacteals: between these two layers the lymphatics anastomose very
freely by means of numerous branches (Langer).
The lacteals are lined with an epithelioid layer and traversed by
connective-tissue trabeculae, which have a like covering. The lacteals
are not simple but in the form of a coarse network (Fig. 189) (Langer).]
[Illustration: Fig. 190.
Isolated fold of mucous membrane of small intestine of _Rana
temporaria_; after Langer. Forty times natural size. Blood-vessels
striped, lacteals shaded. ]
(7) [The *nerves* of the small intestine (p. 200) usually follow the
arteries to the muscular coats, between which they form a plexus
(Auerbach’s plexus); from this numerous twigs are given off, which
course alone or in company with vessels to the mucous coat, where
a second plexus (Meissner’s plexus) is formed. Auerbach’s plexus,
according to Klein, consists of bands of nervous fibrils in endothelial
sheaths; they branch and inosculate, and thus form a plexus. Where
several such branches meet, a more or less complicated decussation of
the bands of fibres takes place. Along these nervous bands are ganglion
cells, either isolated or in groups. The cells are large, generally
spherical, and contain a sharply outlined nucleus with a single or
double nucleolus. The smaller cells generally appear to possess only
one process, which can be traced from the protoplasm of the cell
between the fibrils of the nerve-trunk. The larger cells are distinctly
multipolar, their protoplasm being provided with a number of fine
processes, or, as is oftener the case, with one large and several small
processes. In many instances Klein was able to distinguish around the
ganglion-cells a capsule of a spherical or ovoid shape. In these cases
the body, as well as the processes of the ganglion-cell, were lying
within the capsule. This system of ganglion-cells is in connection with
the individual bundles within the nerve-trunks.
[Illustration: Fig. 191.
Transverse section of a fold of the mucous membrane of _Rana
temporaria_; after Langer. Sixty times natural size.
_A_ Lacteals with transverse trabeculae.
_B_ Circular muscular layer.
_C_ Longitudinal muscular layer.
Blood-vessels striped.
]
Klein describes a second system of ganglion-cells, situated in meshes,
which are formed by the nerve-trunks of the plexus itself. These
ganglion-cells are much larger than the former, and are multipolar;
their protoplasm, which is distinctly fibrillar, with granules between
the fibrils, is provided with one or two long, thick processes and
several short and thin ones; generally the processes are branched. The
general shape of the cells is oblong, the thick, long processes being
commonly at the two opposite poles. The cells are generally isolated,
sometimes situated in the centre of a mesh, or more commonly near a
nerve-trunk that borders the mesh on one side. Each ganglion-cell is
connected with a nerve-trunk of the plexus by at least one process. In
a few of the nerve-trunks of the general plexus, isolated medullated
nerve-fibrils are seen to pursue an almost straight course from one
trunk into another and divide into two. There is no connection between
these medullated fibres and the ganglion-cells.
*Auerbach’s plexus* is a much finer plexus than that just described,
and the ganglia are much smaller. It supplies twigs to the _Muscularis
mucosa_; these break up into fine fibrils, which follow the direction
of the muscle-fibres; other twigs supply the blood-vessels, with which
they can be traced into the bases of the folds of mucous membrane.
Thanhoffer has recently (_l. c._) described nerve-fibrils, which
terminate in the mucous epithelium.]
D. The _Large Intestine_ (Fig. 184 _R_).
[Illustration: Fig. 192.
From a transverse section of the large intestine of _Rana temporaria_,
moderately distended.--G. H.
_A_ Denser portion of submucous coat.
_B_ Looser portion of submucous coat.
_C_ Artery, cut obliquely.
_D_ Circular muscle-layer.
_E_ Longitudinal muscle-layer.
]
*a.* *General description.* The large intestine is a flask-shaped
viscus, lying in the median line. The small intestine opens into it
by an abrupt curve at its anterior end. The large intestine is the
widest part of the alimentary canal, is thin-walled, and diminishes in
width towards its hinder end, where it opens into the cloaca above the
opening of the bladder.
*b.* [*Minute structure.*
(1) The *serous coat* resembles that of the small intestine, etc.
(2) The *muscular coats* resemble those of the small intestine, but are
thinner; the longitudinal layer is, however, proportionally thicker
(Wiedersheim).
(3) The *submucous coat* (Fig. 192) resembles that of the small
intestine in its general structure; the portion lying immediately
beneath the mucous membrane (_B_) is denser in structure.
This layer has no _Muscularis mucosa_.
(4) The *mucous coat* (_A_) is a simple layer of large, columnar,
epithelial cells, with large oval nuclei. The cells have a hyaline
free border, but this possesses no striation. The mucous membrane is
usually described as possessing numerous simple follicles (glands
of Lieberkühn); in those specimens which I have examined they have
been entirely absent (Figs. 192, 193). At six to eight points in a
transverse section of a rectum moderately distended the submucous coat
is thinner, and so throws the mucous coat into slight, longitudinal
grooves; but these do not in the least resemble the glands of
Lieberkühn.
[Illustration: Fig. 193.
Transverse section of large intestine of _Rana esculenta_; the mucous
membrane thrown into longitudinal folds in consequence of the organ
being contracted. Arteries injected with carmine.--G. H.
_A_ Large circular vessels within the muscular coats.
_B_ Fine anastomosis to the mucous coat.
]
(5) The epithelium possesses goblet- or chalice-cells (Hoffmann),
the number of which probably depends upon the period of the year and
the state of digestion. In the rectum, from which the section for
the figures 192 and 193 were cut, not one goblet-cell was found in a
complete series of sections.
If the rectum be contracted, the mucous membrane is thrown into
longitudinal folds.
(6) The *blood-vessels* (Fig. 193) have a simple arrangement. The
arteries are large, and form oblique loops around the intestine, lying
under the peritoneum; from these branches are given off to form a
series of rings in the submucous membrane (Fig. 193 _A_); from these
fine twigs are given off to form a fine anastomosis under the mucous
membrane (_B_).
(7) The *lymphatics* of the large intestine are arranged in two chief
systems: one under the serous coat resembles the corresponding system
of the small intestine. The second set forms a network of rounded loops
in the submucous coat, which give rise to a secondary set of smaller
vessels towards the mucous membrane; this secondary system forms a sort
of trellis-work standing on the rounded loops, and so maps out small
blocks of the thick submucous coat. Towards the cloaca the arrangement
is simpler; the secondary lymphatics are lost, while the primary
lymphatics tend to form elongated, longitudinal loops (Langer).]
II. THE GLANDS CONNECTED WITH THE INTESTINAL CANAL.
A. The *Liver* and *Gall-bladder*.
*a.* *External form.*
(1) The liver (Figs. 185, 194) is a large, reddish-brown organ,
occupying a large part of the anterior abdominal region. It consists
of three or more lobes, which present many individual variations; as a
rule there are two larger lateral lobes (_L_ and _L^1_), and a smaller
median lobe (_L^2_). Each lobe has a superficial or ventral surface,
which is convex, and a deep or dorsal surface, which is concave and
directed towards the other abdominal viscera lying above the liver. The
two surfaces of each lobe meet to form a sharp border around the lobe,
except where the three lobes are more intimately attached, opposite the
apex of the heart (Figs. 185, 194); at this place each lobe possesses a
small, flat, or slightly concave anterior surface.
The left lobe (_L_) hides the greater portion of the stomach, and has
near its inner border a deep fissure, which runs forwards and so marks
off a more or less well-marked fourth lobe. The anterior portion of the
left lobe is attached to the corresponding portion of the right lobe by
a narrow commissure.
[Illustration: Fig. 194.
The liver, seen from the ventral surface.
_Du_ Duodenum.
_H_ Heart.
_L_ Left lobe of liver.
_L^1_ Right lobe of liver.
_L^2_ Middle lobe of liver.
_M_ Stomach.
]
The median lobe (_L^2_) extends backwards as far as the pylorus, and
covers the commencement of the intestine together with the pancreas;
these organs can, therefore, not be seen until this lobe is displaced.
A fifth lobe is sometimes found on the dorsal surface of the median
lobe, and to it or to the dorsal surface of the median lobe the small
intestine is attached by the _Ligamentum hepato-duodenale_ (Fig. 195
_Lhp_). The _Vena portarum_ enters the liver behind this ligament.
The right lobe extends much further dorsalwards than the left lobe, and
even comes in contact with the lung, the vessels of which sometimes
indent its surface in spirit specimens. This lobe is also in contact
with the base of the fat-body, and in females with the oviduct.
By drawing the lobes of the liver to either side and displacing the
heart towards the head, the posterior caval vein is seen passing from
the liver to the heart, and the hepatic commissure joining the lateral
lobes is brought into view.
(2) The *gall-bladder* (Fig. 195 _G_) is placed on the dorsal surface
of the liver in the deep niche between the right and left lobes; it is
attached to the liver by connective-tissue and peritoneum.
The gall-bladder is round or oval in form; when moderately full it has
a smooth, outer wall, which is thin and allows the green colour of the
bile to be seen. It possesses a duct (_Dcy_), the cystic duct (_Ductus
cysticus_), which bifurcates near its origin.
The two cystic ducts (Fig. 195 _Dcy_) join the larger hepatic ducts,
as shown in the figure, and so form a simple anastomosis, from which
three branches (3) of varying size unite at the anterior extremity of
the pancreas to form the common bile-duct (_Ductus choledochus_, _Dc_).
The common bile-duct runs through the whole length of the pancreas,
receiving near its origin additional hepatic ducts (_Dh^1_) from the
middle lobe of the liver. In this course the duct lies either on the
ventral surface of the pancreas or under a thin layer of the glandular
tissue; it receives the ducts of the pancreas and leaves that organ
at its posterior border as a round and strong canal (_Dc^1_). The
duct courses in the gastro-duodenal ligament, and reaches the dorsal
surface of the duodenum at a very acute angle; it then pierces the wall
obliquely and terminates with a slit-like or elongated oval opening.
[Illustration: Fig. 195.
The pancreas and bile-canals. The liver has been displaced towards the
head.
_Dc_ Common bile-duct.
_Dc^1_ Common bile-duct after leaving the pancreas.
_Dc^2_ Opening of the common bile-duct into the duodenum.
_Dcy_ Cystic ducts.
_Dh_ Hepatic ducts.
_Dh^1_ Supplementary hepatic ducts from the middle lobe
of the liver.
_Du_ Duodenum.
_G_ Gall-bladder.
_L_ Left lobe of the liver.
_L^1_ Right lobe of the liver.
_L^2_ Middle lobe of the liver.
_L^3_ Fourth lobe of the liver.
_Lhp_ Gastro-hepatic ligament.
_M_ Stomach.
_P_ Pancreas.
_Py_ Pylorus.
_P^1_ Ducts of the pancreas.
]
*b.* [*Minute structure.*
(1) The *liver* is composed of various tissues: it possesses a
peritoneal covering, a fibrous covering, which supplies trabeculae to
support the various other tissues, blood-vessels, hepatic cells or true
liver parenchyma, and bile-canals.
α. The *peritoneal covering* of the liver encloses the organ almost
completely, the only exceptions being where the various attachments
of the liver are found (see peritoneum). The peritoneal covering of
the liver is for the most part composed of flattened, ciliated cells
(Neumann and Grunau); on the middle lobe these are, however, more or
less replaced by non-ciliated cells. The thickness of these cells
varies considerably, according to the amount of distension to which the
liver is subjected.
β. The *fibrous covering* of the liver is very thin and very difficult
to demonstrate; it consists of connective-tissue fibres with very few
corpuscles. This covering is prolonged into the liver along the portal
canals, where traces of connective-tissue can always be made out.
From these processes and from the whole of the inner surface of the
general connective-tissue capsule are given off fine trabeculae, in
which it is very difficult to find any nuclei; these trabeculae are
everywhere extremely delicate and difficult to demonstrate; nowhere do
they form distinct boundaries between lobuli: the structure closely
resembles the sustentacular tissue of a lymphatic gland (Eberth).
γ. The *blood-vessels* to the liver are the portal vessels (p. 249) the
hepatic veins (p. 247), and the hepatic artery[74] (p. 233)
[Footnote 74: See Plate II, Fig. 196.
I. Partial injection of the liver from the portal vein (blue): _Rana
esculenta_.--G. H.
II. Partial injection of the liver from the hepatic vein (red): _Rana
esculenta_.--G. H.
III. Complete injection of the liver from the hepatic artery (red) and
from the portal vein (blue): _Rana esculenta_.--G. H.
_A_ Portal (interlobular) veins and their branches.
_B_ Hepatic (intralobular) veins and their branches.
_C_ Hepatic arteries and their branches.
]
(1) The portal vessels pass into the liver on its ventral surface; they
divide into branches which course along the middle parts of each lobe
and give off smaller branches in all directions towards the periphery;
the interlobular branches (Fig. 196 I) forming a very complex capillary
network. As compared with the hepatic veins (Fig. 196 II), the
interlobular veins do not give off their capillaries so abruptly, but
tend to supply these from small lateral branches. The portal veins are
accompanied in their course by branches of the hepatic artery, and
often by larger bile-ducts, and thus form portal canals. In no part do
the portal (interlobular) veins or their branches limit the lobules
by distinct rings of vessels, as seen in many higher animals. The
interlobular veins and intralobular veins simply interdigitate with
each other.
(2) The hepatic veins (Fig. 196 I and II) also course chiefly in the
middle parts of the lobes of the liver; they branch, and ultimately
supply intralobular veins which interdigitate with the interlobular
veins (I and II). The capillaries arise very abruptly from an
intralobular vein, and form a network of vessels communicating very
freely with the corresponding capillaries of the interlobular veins.
(3) The hepatic arteries (Fig. 196 III) break up into small branches
which, as a rule, course along the portal canal until near the surface
of the liver, when they leave the portal veins and pass to the surface
to supply the coverings of the liver. In their course along the portal
canals they supply a few very small twigs to the structures forming the
canals. At the surface of the liver the branches of the hepatic artery
form capillaries, which empty themselves into the general capillary
anastomosis beneath (Fig. 196 III).
δ. The *liver-cells* (Figs. 197, 198) are large, and of compressed
spheroidal or polygonal shape. They possess no cell-wall, have usually
one but sometimes two large nuclei, each with a distinct nucleolus.
The cells often contain granules of glycogen or fat-globules. The main
fibrillae of the intercellular network are arranged so as to extend
between a bile-capillary and a blood-capillary (Fig. 197).
ε. The *bile-ducts* (Fig. 198) commence as fine tubes between the
liver-cells, where they are simply small spaces enclosed by the hepatic
cells; they are usually enclosed by three or four cells, possibly
sometimes by only two cells (Hering). Such bile-capillaries are usually
separated from a blood-capillary by the thickness of one liver-cell
only (Fig. 198).
As a number of such bile-capillaries run together to form a larger
duct, the cells enclosing them change their character, becoming
flattened and broader; these cells may, however, be traced continuously
into the true hepatic cells (Hering and Eberth). The bile-duct so
formed then obtains a slight covering of fibrous tissue, which rapidly
increases in quantity, courses along a portal canal, and receives other
ducts on the way; the epithelium lining it gradually becomes more
elongated, and ultimately resembles that found in the common bile-duct
or the gall-bladder.
In the larger ducts the epithelium is, according to v. Brunn,
ciliated; they also possess a layer of unstriated muscle-fibre
(Eberth).]
[Illustration: Fig. 197
Liver-cells, after Kupffer.]
ζ. The *pigment* of the liver varies very much in amount and character,
according to the time of the year and state of health of the animal.
According to Eberth the pigmentary masses are of about the same size as
the white blood-corpuscles, and are possessed of the power of amoeboid
movement (in young animals). The cells possess two to seven nuclei and
vary much in colour and distribution. As a rule the larger the amount
of pigment in a given liver the smaller is the number of fat-globules
found in the individual liver-cells (Eberth).]
[Illustration: Fig. 198.
The bile-capillaries; natural injection with sulphindigotate of sodium:
v v v represent blood-capillaries.--G. H.]
(2) [The *gall-bladder* and *bile-ducts*. The gall-bladder has four
coverings.
α. A serous coat of peritoneal endothelium.
β. A muscular coat, containing unstriated muscle-fibres and
connective-tissue.
γ. A sub-mucous coat of areolar-tissue.
δ. An internal lining of columnar epithelium.
ε. The walls of the gall-bladder are richly supplied with blood-vessels
from the cystic arteries (p. 233); these form a close network in the
submucous coat.
ζ. The muscular and submucous coats also possess a rich nervous plexus,
which contains ganglia and resembles Auerbach’s plexus of the intestine
(Popoff, Gerlach).]
B. The *Pancreas* (Fig. 199 _P_).
*a.* *General description.* The pancreas is a flattened, light
yellowish-brown organ, placed in the loop of the duodenum between this
latter and the stomach. The whole organ is within the gastro-duodenal
ligament, and is attached to the liver; hence it is little influenced
by changes in the amount of distension of the stomach or intestine.
[Illustration: Fig. 199.
The pancreas and bile-canals. The liver has been displaced towards the
head.
_Dc_ Common bile-duct.
_Dc^1_ Common bile-duct after leaving the pancreas.
_Dc^2_ Opening of the common bile-duct into the duodenum.
_Dcy_ Cystic ducts.
_Dh_ Hepatic ducts.
_Dh^1_ Supplementary hepatic ducts from
the middle lobe of the liver.
_Du_ Duodenum.
_G_ Gall-bladder.
_L_ Left lobe of the liver.
_L^1_ Right lobe of the liver.
_L^2_ Middle lobe of the liver.
_L^3_ Fourth lobe of the liver.
_Lhp_ Gastro-hepatic ligament.
_M_ Stomach.
_P_ Pancreas.
_P^1_ Ducts of the pancreas.
_Py_ Pylorus.
]
The organ may be completely exposed by either of two methods: in
the former, the liver, stomach, and duodenum are drawn towards the
head and the dorsal surface of the organ so exposed. In the second
method the liver is drawn backwards, the various peritoneal folds
which connect the duodenum with the posterior border of the liver cut
through, and the three organs then separated; the pancreas can then be
conveniently examined.
The size and shape of the pancreas are subject to great variations
in different specimens. The usual shape of the organ is somewhat
triangular (Fig. 199), the left border being usually unbroken, while
the other two shorter borders are broken into lobes. The longest lobe
stretches as far as the pylorus (_Py_), to which it is attached by
connective-tissue: the opposite extremity of the gland is attached to
the liver.
The excretory duct of the pancreas (_Ductus Wirsurgianus_) opens into
the common bile-duct at about the middle of the pancreas (_P^1_); other
smaller ducts may open into the same canal.
*b.* *Minute structure.* [The pancreas consists of a number of lobes
loosely held together by connective-tissue; each lobe is composed of
a number of lobules attached to each other much more intimately. The
lobules are made up of tubes lined by a single layer of glandular
epithelium. This epithelium is, as a rule, broadly columnar, but in the
smaller tubes may be cubical or polygonal. Each cell has a cell-wall,
nucleus, and very granular protoplasm; the latter shows two zones (in
the inactive condition), a granular zone near the lumen, and an outer,
clear, and finely striated zone (Nussbaum). The lumen of each alveolus
is very small, and in many cases difficult to make out.
The smallest ducts have no special lining, and are therefore bounded
by the glandular cells; the larger ducts have a flattened, cubical
epithelium, which when seen from the surface has an appearance as if
the individual cells were widely separated from one another; these
ducts have a considerable layer of connective-tissue around them. The
largest ducts are lined with a layer of columnar, ciliated epithelium;
the cilia are very long, usually of about the same length as the cell,
sometimes appearing to be even longer. This epithelium is continuous
with the ciliated, epithelial layer of the common bile-duct, which
it resembles. These largest ducts have an extremely thick layer of
connective-tissue around them.
The pancreas and its ducts are very richly supplied with vessels
and nerves; the nerves forming everywhere a fine plexus, the larger
strands of which usually, but not always, course with the larger
blood-vessels. The larger ducts have an especially rich supply of
nerves, of which fibrils may be traced towards the ciliated epithelium;
an anatomical connection between the two has not, however, been made
out.]
III. THE SPLEEN.
*a.* *General description.* Although the spleen belongs to the
lymphatic system, it is considered here in order to complete the
description of the abdominal viscera. It is a small, rounded-oval body,
of a reddish-brown colour, suspended in the mesentery near the anterior
end of the large intestine (Fig. 184 _Mz_). In medium-sized animals
the longer diameter is about 6 mm., and is parallel with the long axis
of the body; the shorter diameter is about 5 mm., and the thickness
varies from about 3 mm. to 4 mm. The dorsal surface is flat or slightly
concave (_Hilus lienis_), and receives the relatively large afferent
and efferent vessels; the rest of the organ is smooth and rounded, and
with its greatest convexity directed towards the left side.
*b.* [*Minute structure.* The structure of the spleen resembles that of
higher animals. It possesses a *serous coat* of peritoneum, under which
is a *fibrous coat*; the latter sends in trabeculae, which divide and
form a fine meshwork of supporting-tissue; the finest trabeculae are
formed by the processes of the connective-cells of the sustentacular
structure. According to Hoffmann, the thickness of the fibres averages
0.001 to 0.011 mm.; the intervening spaces measure 0.002 to 0.012 mm.
The spaces are filled by the spleen pulp, which consists of true
spleen-corpuscles, blood-corpuscles, and pigment-corpuscles.
The *spleen-corpuscles* have an average diameter of 0.006 mm., and are
round or of a rounded oval form. Each consists of a nucleus, with a
very small amount of adherent protoplasm; the nucleus possesses one or
two nucleoli. Some of these cells contain a brownish or black pigment
in granules, but most of them are colourless (Hoffmann).
The *pigment-cells* equal the white blood-corpuscles in size, and
exactly resemble the corresponding pigment-cells of the liver.
The *blood-corpuscles* are found in various stages of disintegration
and regeneration.
The *arteries*, on entering the spleen, at once break up into branches
which pass in all directions, giving off twigs on all sides and at
varying angles; from these capillaries are supplied, which traverse the
parenchyma in all directions. The capillaries empty themselves partly
into veins, partly into the splenic spaces.
The *veins* commence either as capillaries in connection with
the arteries or by communicating with the splenic spaces. This
communication is brought about by small twigs of about 0.015 mm.
diameter, which have incomplete walls, and so open into the splenic
spaces (Hoffmann).
*Malpighian bodies* are represented by collections of splenic cells on
various arterial twigs; they are, however, not so sharply defined as is
the case in some higher animals.]
IV. THE PERITONEUM.
*a.* *General description.* The *peritoneum* is a thin, pigmented
membrane lining the abdominal cavity. Tracing it forwards from the
ventral wall of the abdomen (_Peritoneum parietale_), it can be
followed along the deeper surface of the muscles to the pericardium.
The middle portion leaves the abdominal wall by accompanying the
anterior abdominal vein; the lateral portions are continued further
forwards, and then ascend on the pericardium and the deeper surfaces of
the lateral walls in the thoracic region.
The peritoneum passes thence to the ventral surface of the liver
(_Ligamentum coronarium_), covers this surface and passes on to the
dorsal surface of the organ, which, together with the gall-bladder,
it completely encloses. The membrane thus reaches the dorsal wall
(_Ligamentum suspensorium hepatis et pericardii_); from the lateral
borders of the liver it passes upwards to the dorsal wall, and thus
forms a pocket-like pleuro-peritoneal cavity on either side.
From the dorsal wall and above the attachment of the coronary ligament
of the bladder the peritoneum reaches the root of the lung on each
side, and completely invests the organ: while in the middle line it
covers the outer surface of the oesophagus and attaches it to the
dorsal wall, thus forming the first part of the mesentery.
Just behind the root of the lung, the peritoneum, in female specimens,
has an opening on each side (_Ostium abdominale tubae Fallopiae_), by
which the oviduct communicates with the peritoneal cavity.
Tracing the peritoneum backwards, it passes over the ventral surface
of the kidneys so as to exclude them from the peritoneal sac: in the
middle line, between the kidneys, the peritoneum descends to form the
mesentery for the small intestine. At the inner borders of the kidneys,
the testes or ovaries are pushed into the abdominal sac, and so possess
well-marked mesenteries; the mesovarium becomes longer towards the
cloaca, but attains its greatest development in the breeding season,
when it is arranged in numerous folds. Along the outer borders of the
kidneys, in females, the peritoneum again descends into the abdominal
cavities to enclose the oviducts, which have broad mesenteries. Towards
the rectum these mesenteries are shorter and attached to either side
of the bladder by a well-marked free border: as the middle line of
the bladder is attached by the peritoneum to the rectum, two distinct
pouches (_Cava recto-vesicalia_) are formed, which descend deeply
into the pelvic cavity. The upper walls of these pouches are pushed
in between the urostyle and the rectum, and together form a strong
meso-rectum, which is longer near the _Valvula Bauhinii_ and continuous
with the mesentery of the small intestine. The hinder portion of this
mesentery is very short, and only covers the lateral walls of the
rectum.
With the exception of a small portion of its dorsal surface, which is
attached to the rectum, the whole surface of the bladder is covered
with peritoneum.
The mesentery of the alimentary canal commences in connection with
the oesophagus between the roots of the lungs; it is attached to the
dorsal surface of the liver, covering the posterior caval vein, and is
attached to the gall-bladder. From this point it extends, as a free,
arched fold, to the concave right border of the stomach, which is
completely surrounded by peritoneum.
The gastro-duodenal fold (_Ligamentum gastro-duodenale_) extends
from the stomach to the pylorus and includes the pancreas. The
hepato-duodenal fold (_Lig. hepato-duodenale_) extends from the portal
fissure of the liver to the duodenum.
The mesentery of the small intestine is broad and arranged in folds,
which follow the curves of the intestine; and is attached in the middle
line, immediately beneath the vertebrae, where it encloses the aorta.
The various folds and mesenteries carry the blood-vessels and nerves
to the different organs; in this course the vessels are surrounded by
large lymphatics, which communicate with each other.
[Illustration: Fig. 201.
Preparations from the peritoneum of _Rana esculenta_.--G. H.
I. From peritoneum of the ventral wall of abdomen, stained with silver
and logwood (Hartnack, Oc. I, Syst. 7).
II. From mesentery of small intestine of _Rana esculenta_, stained with
silver (Hartnack, Oc. I, Syst. 7).
III. Preparation to show ciliated cells between non-ciliated cells;
after Neumann. IV. Vertical section at border of liver to show ciliated
epithelium; after Neumann.
_A_ Stoma.
_B_ Pigment-cells.
_C_ Ciliated cells.
_D_ Non-ciliated cells.
]
*b.* *Minute structure* (Fig. 201).
[The peritoneum is a serous membrane, formed for the most part of a
layer of irregular endothelial cells, arranged on a thin layer of
subserous, connective-tissue (Fig. 201 I, II, and III).
The endothelial cells are attached to each other by cement-substance,
easily stained by silver nitrate. The cells covering the general
surface of the peritoneal cavity are larger and broader than those
covering the mesentery of the small intestine (compare I and II,
Fig. 201).
At various points stomata are found, bordered by smaller and more
deeply staining epithelium (I, _A_). The membrane covering the general
cavity is also much more pigmented than that covering the mesentery
(compare I and II).
Various portions of the peritoneal surface possess ciliated cells,
and these cells are usually thicker than the surrounding non-ciliated
cells. Such cells are found especially near the openings of the
oviducts and on the liver. The dimensions of the cells vary; according
to Neumann the average dimensions of ciliated cells on the liver
are: 0.006 mm. depth (without the cilia); nucleus, 0.012 mm. long
and 0.003 mm. broad. The cells are five- or six-sided and bounded by
straight sides (Neumann).]