in vivisections; but Longet has further shown that dogs with an opening into the trachea are frequently able to run and leap with "astonishing agility." He also saw a horse, with a large canula in the trachea, that performed severe labor and drew heavily-loaded wagons in the streets of Paris.1

Passive Organs of Locomotion.

It would be out of place to describe fully and in detail all of the varied and complex movements produced by muscular action. Many of these, such as the movements of deglutition and of respiration, are necessarily considered in connection with the functions of which they form a part; but others are purely anatomical questions. Associated and antagonistic movements, automatic and reflex movements, etc., belong to the history of the motor nerves, and will be fully considered under the head of the nervous system.

The study of locomotion involves a knowledge of the physiological anatomy of certain passive organs, the bones, cartilages, and ligaments. Though a complete history of the structure of these parts trenches somewhat upon the domain of anatomy, we are tempted to give a brief description of their histology, as it will complete our account of the tissues of the body, with the exception of the nervous system and the organs of generation, which will be taken up hereafter.

Locomotion is effected by the muscles acting upon certain passive, movable parts. These are the bones, cartilages, ligaments, aponeuroses, and tendons. We have already described the fibrous structures, and it only remains for us to study the bones and cartilages.

Physiological Anatomy of the Bones.-The number, classification, and relations of the bones are questions belonging to descriptive anatomy; and the only points we propose to consider refer to their general or microscopic structure.

1 LONGET, Traité de physiologie, Paris, 1869, tome ii., p. 669.

Every bone, be it long or short, is composed of what is called the fundamental substance, marked by microscopic cavities and canals of peculiar form. The cavities contain corpuscular bodies, called bone-corpuscles. The canals of larger size serve for the passage of blood-vessels, while the smaller canals (canaliculi) connect the cavities with each other, and finally with the vascular tubes. Many of the bones present a medullary cavity, filled with a peculiar structure, called marrow. In almost all bones there are two distinct portions: one, which is exceedingly compact, and the other, more or less spongy or cancellated. The bones are also invested with a membrane, containing vessels and nerves, called the periosteum.

The method usually employed in the study of the bones is by thin sections made in various directions, and examined either in their natural condition or with the calcareous matter removed by maceration in weak acid solutions. By the first method, we can make out the relations of the fundamental substance, the direction and relations of the vascular canals, and the form, size, relations, and connections of the bone-cavities and small canals. By the latter method we can isolate and study the organic and corpuscular elements.

Fundamental Substance.-This constitutes the true bony substance, the medullary contents, vessels, nerves, etc., being simply accessory. It is composed of a peculiar organic matter, called osteine, combined with various inorganic salts, in which the phosphate of lime largely predominates. In addition to the phosphate of lime, the bones contain carbonate of lime, fluoride of calcium, phosphate of magnesia, soda, and the chloride of sodium. The relative proportions of the organic and inorganic matters are somewhat variable; but the average is about one-third of the former to two-thirds of salts. This proportion is necessary to the proper consistence and toughness of the bones.

Anatomically, the fundamental substance is arranged in the form of regular, concentric lamellæ, about 3 of an

inch in thickness.' This matter is of an indefinitely and faintly-striated appearance, but it cannot be reduced to distinct fibres. In the long bones the arrangement of the lamellæ is quite regular, surrounding the Haversian canals, and forming what are sometimes called the Haversian rods, following in their direction the length of the bone. In the short, thick bones the lamella are more irregular, frequently radiating from the central portion to the periphery. These peculiarities in the disposition of the fundamental substance will be more readily understood after a description of the Haversian canals.

Haversian Canals.-These canals exist in the compact bony structure. They are absent, or very rare, in the spongy and reticulated portions. Their form is rounded or ovoid, the larger ones being sometimes quite irregular. In the long bones their direction is generally longitudinal, although they anastomose by lateral branches. Each one of these canals contains a blood-vessel, and their disposition constitutes the vascular arrangement of the bones. They are all connected with the opening on the surface of the bones, by which the arteries penetrate and the veins emerge. Their size, of course, is variable. According to Sappey, the largest are about and the smallest of an inch in diameter. Their average size is from to of an inch. In a transverse section of a long bone the Haversian canals may be seen cut across and surrounded by from twelve to fifteen lamellæ. In'a longitudinal section the course and anastomoses may be studied.

Lacuna.-The fundamental substance is everywhere marked by irregular, microscopic excavations, of a peculiar form, called lacunæ, or osteoplasts. These were at one time supposed to be corpuscles of calcareous matter, and were known as the bone-corpuscles; but it has since been ascertained that this appearance is due to the imperfect methods 1 SAPPEY, Traité d'anatomie, Paris, 1866, tome i., p. 84. 2 SAPPEY, op. cit., p. 76.

of preparation of the thin sections of bone. They are connected with numerous little canals, giving them a stellate appearance. These are most numerous at the sides. The lacunæ measure from to of an inch in their long diameter, by about of an inch in width.' They contain the true bone-corpuscles, which we will presently describe.

Canaliculi.-These are little wavy canals, connecting the lacunæ with each other and presenting a communication between the first series of lacunæ and the Haversian canals. Each osteoplast presents from eighteen to twenty canaliculi radiating from its borders. Their length is from to bo of an inch, and their diameter about of an inch. The arrangement of the Haversian canals, lacunæ, and canaliculi is shown in Fig. 19.

Vascular canals and lacunæ, seen in a transverse section of the diaphysis of the humerus. Magnified two hundred diameters.-1, 1. 1, Section of the Haversian canals: 2. Section of a longitudinal canal divided at the point of its anastomosis with a transverse canal. Around the canals, cut across perpendicularly, are seen the lacune (with their canaliculi), forming concentric rings. (SAPPEY, Traité d'anatomie, Paris, 1866, tome i., p. 79.)

Bone-cells or Corpuscles.-By treating perfectly-fresh specimens of bone with weak acid solutions, Virchow has * Idem., p. 81.

1 SAPPEY, op. cit., p. 80.

demonstrated the presence of stellate cells, or corpuscles, exactly filling up the lacunæ, and sending prolongations into the canaliculi.' These structures have since been studied by Rouget, who has succeeded in demonstrating them in fresh bones from the foetus, without using any reagent." They are stellate, granular, with a large nucleus and several nucleoli, and are of exactly the size and form of the lacunæ. They send out prolongations into the canaliculi, but it has been impossible to ascertain positively whether or not they form membranes lining the canaliculi through their entire length.

Marrow of the Bones.-The peculiar structure called marrow is found in the medullary cavities of the long bones, filling them completely and moulded to all the irregularities of their surface. It is also found filling the cells of the spongy portion. In other words, with the exception of the vascular canals, lacunæ, and canaliculi, the marrow fills all the spaces in the fundamental substance. We know very little of the functions of the marrow, and will therefore pass it over with a brief description.

It is now settled that the cavities of the bones are not lined with a membrane corresponding to the periosteum, and that the marrow is applied directly to the bony substance. In the foetus and in very young children, the marrow is red and very vascular. In the adult it is yellow in some bones, and gray or gelatiniform in others. It contains certain peculiar cells and nuclei, with amorphous matter, adipose vesicles, connective tissue, blood-vessels, and nerves.

Medullocells.-Robin has described little bodies, existing both in the form of cells and free nuclei, called medullocells. These are found in greater or less number in the bones at

1 VIRCHOW, Cellular Pathology, Philadelphia, 1863, p. 112. Virchow's first observations were made in 1850.

' ROUGET, Note sur les corpuscles des os.-Journal de la physiologie, Paris, 1858, tome i., p. 764, et seq.