Page:Encyclopædia Britannica, Ninth Edition, v. 1.djvu/972

Rh 908 tlielial cells; but if it becomes an artery or a vein, a further differentiation of the mesoblast cells into the muscular and elastic coats and the tunica adventitia takes place. The heart appears immediately below the head in the form of a collection of cells in the splanchnopleure layer of the mesoblast. It is believed that these cells form in the first instance a solid mass, the central part of which liquefies to form blood and blood-corpuscles, whilst the peripheral cells form the wall of a tube. The heart tube now presents two constrictions, which indicate its division into an auricle, a ventricle, and a lulbus arteriosus. The single ventricle then subdivides into two by the gradual growth of the septum from the apex to the base, and about the eighth week of embryo-life the right and left ventricles are com pletely separated from each other. A septum then begins to form in the originally single auricle, but its growth is not completed until after the birth of the child, so that during foetal life the cavities of the right and left auricles communicate with each other through a hole in the septum, named foramen ovale. The primitive aortce, right and left, arise from the ductus arteriosus, and extend up wards to the 1st pair of visceral arches, into which they pass and arch backwards to the sides of the spinal column, where they form the dorsal aortce. Four additional pairs of arterial arches then spring from the primitive aortce below the 1st pair, and the whole are enumerated from above downwards as the 1st, 2d, 3d, 4th, and 5th pairs of vascular arches. Each arch communicates behind with the dorsal aorta of its own side. The two dorsal aorta? then approximate and blend with each other to form the descending thoracic and the abdominal aorta. A longitu dinal septum also forms within the bulbus arteriosus itself, which divides it into two vessels : the one, the ascending aorta, becoming continuous with the cavity of the leftventricle ALPHABETICAL CONTENTS. [VASCULAR SYSTEM. and with the 1st, 2d, 3d, and 4th pairs of vascular arches, the other, the pulmonary artery, becoming continuous with the cavity of the right ventricle and with the 5th pair of vascular arches. The 4th left vascular arch enlarges to form the transverse part of the arch of the aorta, and the left subclavian artery springs as a collateral branch from it. The 4th right arch forms the innominate, and the com mencernent of the right subclavian artery. The 3d pair of arches form the two internal carotid arteries ; each com mon carotid is formed from the part of the primitive aorta which connects the 3d and 4th arches with each other ; whilst the external carotid is an enlargement of that part of the primitive aorta which runs upwards from the 3d to the 1st visceral arch. From the 5th left vascular arch, which is now continuous with the pulmonary artery, two collateral branches arise, which proceed one to each lung, and form the right and left pulmonary arteries, whilst the terminal part of this arch joins the end of the transverse part of the arch of the aorta, and forms the ductus arteriosut. During fcetal life, the lungs being inactive, the blood of the right ventricle which passes into the pulmonary artery almost entirely flows through the ductus arteriosus into the aorta. But when the child is born, and the lungs come into play as respiratory organs, then the blood of the right ventricle flows into the lungs through the right and left pulmonary arteries, and the ductus arteriosus, being no longer required, shrivels up into a slender fibrous cord. The capillaries, veins, and lymphatics are also produced by a histological differentiation of the cells of the mesoblast. In order to complete the exposition of the subject, the Digestive, Respiratory, Reproductive, and Urinary systems of organs have still to be considered. These v.ill be dealt with in detail under other headings in the succeeding volumes. (w. T.) Abdominal muscles, 835. Cervical vertebra, 820. Eyelids, 890. Lacteals, 906. Osseous system, 820 ; Sommering, 816, Achillini, 806. Cheek, 825. Fabricius, 809. Leaping, 842. tissue, 853. Special anatomy, 819. Adipose tissue, 851. Cheselden, 815. Face, 825. Leeuwenhoeck, 812. Ovum, 844. Sphenoid bone, 823. Albinas, 814. Chest, 822. Fallopius, 809. Lieutand, 814. Pacinian corpuscles, 862. Spinal cord, 8C5; nerves, Alexandrian school, 801. Chyle, 846. Fat, 851. Life, 843. Palate, 825. 867. Amphiarthroses, 833. Circulation of blood. Femur, 829. Limb, lower, 828; joints Palfyn, 815. Spine, 820; muscles, 835i. Ankle, 830, 841. 899. Fibrous tissues, 850. and muscles, 840 ; up Parietal bone, 824. Splint bone, 829. Aorta, 902. Clavicle, 826. Fibula, 829. per, 826; joints and Patella, 829. Steno, 812. Appendicular skeleton, Coccyx, 821. Fiddlers muscles, 840. muscles, 838. Pauli, 811. Sternum, 822. 826. Collar bone, 826. Fingers, 828; joints of, Lister, J. J., 818. Pecquet, 811. Sutures, 832. Arabian school, 805. Collins, 813. 839. Locomotive organs, 820. Pelvis, 829. Swallowing, 838. Arachnoid mater, 865 Columbus, 809. Foot, 830; joints of, 841. Lumbar vertebrae, 821. Periosteum, 854. Sweat glands, 899. Aranzi, 809. Comparative anatomy, Forehead, 824. Lymph, 846. Perspiration, 899. Tarsus, 830. Aretceus, 802. 799, 813, 818. French school, 807, 816. Lymphatics, 906. Pharynx, 8U7. Taste, 896. Aristotle, 800. Corpuscles, 845. Frontal bone, 824. Malar bone, 825. Pia mater, 865. Temporal bone, 824. Ann, 827 ; joints, 839 Corti, organ of, 894, Galen, 803. Malpighi, 812. Pigment, 851. Terminology, 799. Arteries, 902. Cowper, 813. Genga, 815. JIarinus, 802. Plexus, neiTous, 8G8. Thigh, 829. Articulation, 832. Cranium, 822. German school, 817. Marrow, 854. Polybus, 800. Tibia, 829. Asellius, 811. Craikshank, 815. Glisson, 811. Mascagni, 815. Pons Varolii, 871. Tissues, 842; conne: iva Axial skeleton. 820. Cuticle, 897. Graaf, 812. Maxilla, 825. Portal vein, 906. 849. Berenger, 806. Definitions, 799. Hair, 898. Meckel, 814, 816, 817. Protoplasm, 843. Toes, 830. Bergen, 814. Deglutition, 838. Haller, 814. Medulla oblongata, 870. Pubis, 828. Tongue, 895. Bichat, 816. Development, 830. 842, Hand, 827; joints of, 839. Metacarpus, 828. Quain, 817. Tonsil, 837. Blood, 845; circulation of, 899. 853, 858, 863, 907. Diarthroscs, 833. Harvey, 810. Haunch, 828. Microscope, 817. Mondino, 805. Radius, 827. Respiratory muscle?, 835. Touch, 897. Tympanum, 892 Blood-Tascular alands, Digits, 828; joints of, Head, 822; joints and Monro, 815. Retina, 888. Ulna, 827. 907. 839. muscles, sr,G. Morgagni, 813. Ribs, 822. Uvula, 837. Bone, 853. Dionis, 811. Hearing, 895. Mouth, 837. Ridley, 813. Valsalva, 813. Bonn, 814. Dorsal vertebra;, 821. Heart, 899. Mucous membranes, Ruffus, 802. Varolius, 809. Brain, 864, 869; weight Drum of car, 892. Henle, 817. 847. Running, 8-12. Vascular system, 893; of, 879 Dubols, 807. Herophilus, 802. Muscles, 833. Ruysch, 812. development, U07. Breast-bone, 822. Dura mater, 814. Hewson, 815. Muscular tissue, 856. Sacrum, 821. Veins, 905. Breathing, 835. Duverney, 812. Hip joint, 840. Museums, 819. Santorini, 813. Vertebra;, 820. Bologv.a school, 805. Ear, 891. Hippocrates, 799. Nails, 897. Scapula, 826. Vesalius, 807. Camper, 815. Capillaries, 905. Elbow joint, 5&quot;S. Endothelium, 848. History. 799. Humerus, 827. Neck, 82L Nerves, cerebro-spinal, Scarpa, 816. Secreting glands, 843. Vicussens, 813. Voluntary muscles, 832,. Carpal bones, 827, joints, English school, 817. Hunter, J, 815. 863. Sense organs, 884. involuntary, 856. 839. Epithelium, 847. Hunter, W. 814. Nervous system, 858 ; Serous membranes, 848. Vomer, 825. Cartilage, 851. Erasistratus, 801. Hvoid bone, 825. sympathetic, 883. Servetus, 810. Walking, 841. Cells, 843. Ethmoid bone, 824. Ilium, 828. Nose, 825, 884. Shin, 829. Walter, 81G. Celsus, 602 Etienne, 807. Ischium, 829. Nostrils, 826. Shoulder, 826 ; Joint, 838 Wesling, 811. Cerebellum, 871. Eustachius, 808. Jaw, 825. Nuck, 811. Sight, 889. Wharton. 811. Ccrebro 1 - spinal nerves, Expression, muscles of, Joints, 832. Occipital bone, 823. Skeleton, 820. Willis, 811. 863. 836. Knee, 829, 840. Olfactory nerve, 885 Skin, 847, 897. Winslow, 814. Cerebrum, 872; Internal Eyeball, 8S5; muscles, Lachrymal bone, 825; Optic nerve, 889. Skull, 822. Wrist, 827; joint, 839. structure of, 877 891. gland, 891. Oribasius, 804. Smell, 8S5. Zinn, 814. END OF VOLUME FIRST NSILL AND COMPANY, PRINTERS, EDINBUEQfl.