Chapter XIX: Section V (1)

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.

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.

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).

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.

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.

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.

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).]

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.)]

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).]

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.

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).]

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.

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.
]