ANATOMY
403
by Klein, Quart. Journ. of Micros. Sc. 1875); (2) the thyroid body, which arises as a diverticulum from the fourth branchial cleft on each side and medially from the fundus of a pouch whose opening remains in vestige on the back of the tongue, as in the foramen caecum. It consists essentially of a number of closed follicles lined with epithelium, embedded in a vascular connective-tissue matrix (see Baber, Phil. Trans. 1876 ; Biondi, Archiv. Ital. de Biol. 1892). (3) Em10.—Section of the spleen, seen under a low bedded in the thy- Fig. power. A, fibrous capsule ; b, trabeculae ; c, Malroid are the para- pighian corpuscles ; d, blood-vessels ; e, spleenthyroid bodies, of pulp. which, there are two on each side, differing in the details of structure from the thyroid (see Welsh, Journ. of Anat. xxxii. 292). (4) The thymus, transitory in man, but persistent in other animals, is derived from a diverticulum of the third branchial cleft (see Watney, Phil. Trans. 1882 ; and Symington, Journ. of Anat. xxxii. 278). (5) The suprarenal body, placed above and on the inner side of the kidney. (For its structure see Bolleston, and for the development, Minot, Embryology, p. 485.) (6) Thzpituitary body above the body of the sphenoid is formed partly from the end the terminal part of the duct persists as a short blind tube of the infundibulum of the brain and partly from the lundus which is called Meckel’s diverticulum. The differentiation of the stomodseum. For its structure see Schonemann in of the lower end of the alimentary canal as a large Virchow’s Archiv, 1892. Other structures of the kind intestine begins in the lower vertebrates. That part which are rudimentary in man are (7 ) the carotid gland, and which in the quadruped is lowest and most depending (8) the coccygeal body. (Described by Luschka, Virchow s becomes distended by the accumulation of waste or faecal Archiv, 1860; Reichert’s Archiv, 1862; and Schaper, materials, and when this differentiation is established, the Schultze’s Archiv, 1892. See also Arnold, Virchow’s Archiv, beginning of the large gut 1866.) The haemolymph glands which lie in the hilum of is usually marked by the the kidney are also structures of this class. (See development of a blind Drummond, Journ. of Anat. 1900.) V. The vascular system has been described in vol. i. pouch or caecum. In the human embryo this is a p. 899, and most additions to our knowledge have been tapering conical sac, but in matters of detail. The development of the heart has when, after the assumption been revised by Born. The morphology of the venous of the upright position, the system has been carefully studied in detail by Hochstetter caecum changes its position {Anat. Anz. 1887-88 ; Morpholog. Jahrb. 1891). For the and sinks down on the right arterial system see Eichholz in Journ. of Anat. 1895, side into the iliac fossa, the and Mackay, Proc. Philos. Soc. Glasgow, 188/. The histological elements of blood are described in vol. base of this becomes distended and is called the i. p. 845. It has since been shown that white corpuscles caecum, while the originally do not constitute a homogeneous category, but . BIood fusiform extremity narrows under this name at least six diverse forms are and becomes the vermiform present in healthy blood. The points of difference are appendix (Fig. 9), often the size, shape, and disposition of nucleus; nature of cell Fig. 9.—Caecum and vermiform appendix of human intestine. seat of a painful and danger- reticulum; and composition of the contained granules shown by their different reactions with staining media. ous inflammatory process—another of the penalties we pay as The following are the chief varieties:— for the advantage of the upright position. A series of peculiar glandular masses in the body differ (1) About 70 per cent, of the corpuscles have polymorphic, manyfrom the true secreting glands in having no separate lobed nuclei which often seem to break up into three or four ducts. It is generally believed that these pour distinct masses (hence these have been named polynuclear). The Ductless ppeir secretions directly into the blood, and it is cells are moderately large and stain readily, the protoplasm reacting glands. certain that in most cases disease or ablation of to acid stains while the granules are neutrophile. (2) About 2 per cent, of corpuscles, similar to the last in most aspects, diner bj these organs produces specific effects on the composition o containing a peripheral stratum of granules which stain deeply eosin. (3) About 1 per cent, are mononuclear, of much larger the blood and on local nutrition. These organs aie (1) t e with size, the single nucleus being large, oval, and excentric ; the protospleen (vol. i. p. 907), whose essential structure (Tig. 10) plasm is free from granules and weakly basophile. (4) About 4 per consists of a mass of adenoid connective tissue, with a hbro- cent, of the total are intermediate in characters between those ot muscular capsule, into whose meshes capillary and other the first and third orders ; they are smaller than the typical monoblood-vessels open (a good description of its tissue is given nuclear leucocytes, and have a bilobed nucleus which stains more
vanished, although a rudimental tooth in this position has been described by Fraser as a not uncommon anomaly among black races (Proc. Camb. Philos. Soc. 1900). In the lower races of mankind the teeth are large, and this can be measured by the comparison of the length of the five molar teeth with that of the basicranial axis. The former is over 44 per cent, of the latter in the black races ; under 42 per cent, in the whites. The human soft palate has a uvula (vol. vii. p. 223), which is absent in most mammals. This pendant acts as a sentinel at the passage from the mouth to the pharynx, and is needed because of the upright position of man and because in him the glottis, or top of the air passage, is not prolonged up so as to project into the nasal region of the pharynx above the velum, as it is in the majority of animals. Concerning other parts of the digestive canal, further research on the oesophagus will be found in the papers of Birmingham, Journal of Anat. xxxiii. p. 10, and Strahl, Arch.f. Anal. u. Phys. 1889. Bor the minute structure of the stomach, see Langley, Journal of Phys. 1882, and Muller, Verhandl. d. biol. Verein, Stockholm, 1891-92. For a discussion on the position of the stomach, see Lesshaft in Virchow’s Archiv, 1882. On the caecum see Treves, Hunterian Lectures, 1885. Recent descriptions of the structure of the villi of the small intestine will be found in Paneth, Arch. f. mikrosp. Anat. 1888 ; and on the study of the pancreas see Podrwyszotzky, Arch. f. mikrosp. Anat. 1882. The lobes of the liver and their embryonic relations have been described by Thomson, Journ. of Anat. xxxiii. p. 546 ; on the structure of the liver see Retzius, Biol. Untersuch., Stockholm, 1892, and Shore, Journ. of Physiol. 1889. In the foetal intestine the duct of the umbilical vesicle communicated with the region which becomes in the adult lower part of the small intestine. In intestine. gthe eneraj p. disappears completely, but occasionally
