Page:Encyclopædia Britannica, Ninth Edition, v. 1.djvu/863

Rh HUMAN ANATOMY.] ANATOMY 819 jaw because it exists in other vertebrates, and the announce ment of the theory of the vertebrate nature of the skull by Goethe and Oken, directed anatomists into a line of inquiry which has been productive of fruitful results, and has exercised a great influence on the progress and direction of biological science. Geoffrey St Hilaire and C. Martins in France; Spix, Cams, Gegenbaur, and Haeckel in Ger many; and Owen, Goodsir, Humphiy, Huxley, Parker, and Cleland in Great Britain, have all published important memoirs in this department of anatomical research. The formation of anatomical museums in connection with universities, and elsewhere, by enabling specimens to be accumulated for observation and comparison, has contributed in no small degree to the progress of anatomical science. Pre-eminent amongst these is the collection originally formed by the genius, energy, and self-devoted- ness of John Hunter, which, under the fostering care of the council of the Royal College of Surgeons of England, has been materially augmented in all its departments by a succession of curators Clift, Owen, Quekett, and Flower. The aid which has been afforded to anatomists in the publication of their researches, more especially in providing plates and other expensive means of illustration, by the learned societies of Europe, and the circulation which has been given to their memoirs through the Transactions and Proceedings of these societies, and through the Journals devoted to anatomical and physiological science, have materially contributed to the diffusion of a knowledge of discoveries, and to the general advance of the science. SPECIAL ANATOMY OF THE HUMAN BODY. Man, zoologically speaking, belongs to the Mammalian class of the Verte brate sub-kingdom, i.e., his young are brought forth alive, and nourished during infancy on milk secreted in mammary or milk-forming glands. In common with all vertebrate organisms, he possesses a spine orvertebral column and a skull, in which are contained the brain and the spinal marrow, and on the ventral surface of the spinal column are situated the several sub divisions of the alimentary canal. But man possesses certain special or distinctive anatomical characters. The most noticeable, as seen on an external inspection of his body, is his erect position. He is, indeed, the only liv ing creature that can walk or stand erect, i.e., with the axis of the spine vertical ; with the hip and knee joints capable of being fully extended, so that the leg is brought into line with the thigh; with the foot so planted on the ground that it rests on the heel behind and on the roots of the toes in front ; with the upper limbs so arranged as to act, not as instruments of progression, but of prehension ; and i 7 with the head so balanced on the ton FlG - 1- Diagrammatic sec- c ,i -j.-Lj.jLTf ^ tl0n tarough the human ot tiie spine that the face and eyes head and trunk The look directly to the front. His bones, joints, and muscles are constructed and arranged so as to enable him to preserve the erect attitude without fatigue. In other vertebrata the axis of the spine is oblique or horizontal, the hip and knee joints are perma nently bent at a more or less acute angle, the limbs cor- skull and spine, darkly shaded, and containing the cerebro-spinal nerv ous axis, are dorsal, or at the back. The aliment ary and respiratory tubes, seen in outline, are ven tral, or at the front. The dotted line V represents the vertical axis of the trunk. the spine lies obliquely to the vertical dotted une. (After responding to the human upper extremities, are, in the form of legs, wings, or fins, instruments of progression, and the head is articulated with the spine at or near the hinder end of the skull. Owing to the oblique or horizontal attitude of the body in the vertebrata generally, and its erect position in man, the terms FlG - 2 -~ Outline diagram of a quadruped ; the which are employed in ^e^Kd^f ( ^ h ^fj describing the relative position of different parts are. not used in the same sense by the human and comparative anatomist. Thus, parts which are su perior, or above other parts, in the human body, are anterior, or in front, in other vertebrata; and parts which are posterior, or behind other parts in man, are superior to them in other vertebrata. To obviate the confusion which must necessarily arise when com paring the human body with that of other vertebrates, certain descriptive terms have been recommended which. may be employed whether the positions of the body be erect or non-erect. Thus,, the aspect of parts directed towards the region where the atlas or first vertebra is situated is atlantal, that directed towards the sacrum is sacral, that towards, the back is dorsal, that towards the front ,7 7 i j- j_ ,1 is ventral or /iwmal. Quite recently the term prce-axial has been introduced as equivalent to atlantal, and post-axial to sacral. The body may be considered as divided by an imaginary plane, the mesial plane, into two lateral and similar halves, a right and left, so that it exhibits a bilateral sym metry; and the constituent parts are described as being external or internal to each other, according to their relative position to this plane. For descriptive purposes, also, we may subdivide the body into AXIAL and APPENDICULAK. portions. The AXIAL part is the stock or stem of the body, and consists of the Head, the Neck, and the Trunk. The trunk is again subdivided into the FIO. 4. Outline diagram of n r&amp;gt;lipqf, rvr Thm-mr onrl tlm 1-,p11v nr monkey in the semi -erect &amp;gt;r inoiax, ana tae eiiy or p 0sition. The axis of the spine Abdomen: and the abdomen is lies obliquely to the vertical again subdivided into the abdo men proper and the Pelvis. The axial part contains the organs essential to the preservation of life. In the head is lodged the brain, from which the spinal marrow is prolonged down the spinal canal. At the sides of the head are the ears, and opening on to the face are the eyes, nostrils, and mouth. Prolonged down the neck are the gullet and windpipe, with the latter of which is associated the organ of voice. Within the chest lie the heart, lungs, and gullet; and in the abdomen are contained the stomach, intestine, liver, spleen, pancreas, kidneys, and other organs concerned in the urinary and generative functions. The APPENDICULAR part forms the limbs, which do not contain organs essential to life. In man the limbs are called Upper and Lower the former are instruments of prehen sion, the latter of progression. The subdivisions of the body are not homogeneous in structure, but are built up of several systems of organs, each system, being characterised