cartilage, by subperiosteal ossification, which goes on at the same. time and forms the compact tissue of the shaft. MUSCLE. MUSCULAR STRUCTURE is distinguished by the property of contractility, which is excited by certain stimuli. Two kinds of muscle exist in the animal body, differing from each other in structure and function. 1. Voluntary muscle, which contracts under the influence of the will. 2. Non-voluntary muscle, which acts independently of the will. Examination of Striated or Voluntary Muscle.-For the study of this structure, a portion of boiled beef or horseflesh is to be obtained, and systematically dissected, in order that each of the three parts into which voluntary muscle is divisible may be separately examined, viz.: 1. Fasciculi, which are bundles of fibres; 2. Fibres, which are bundles of fibrilla; 3. Fibrillæ, which appear like rows of fine particles, called 'sarcous elements.' Fasciculi are visible to the unaided eye, constituting the fibres seen in boiled beef. The coarse or fine texture of muscle depends upon the size of the fasciculi, which vary in diameter according to the number of fibres united to form them. By the aid of a common lens the prismatic form of the fasciculi, their variation in size, and general arrangement, may be distinctly Each fasciculus is invested by a sheath of areolar tissue, termed 'Perimysium,' which may be seen in transverse sections, made by drying a piece of half-boiled horseflesh, about three inches long by one inch in diameter, until it will bear the pressure of the razor. Fine sections may then be cut and placed on the slide in a little water; in a short time the natural condition of the tissues is in a great measure restored, and the object may be covered, and viewed with a low power. If the section is sufficiently thin, the fasciculi, with the investing membrane and the ends of the component fibres, will be very distinct. Transverse section from the sterno-mastoid in man; 50 times magnified. Generally the fasciculi run straight from one end of the muscle to the other, excepting in those instances where the tendon extends some distance into the substance of the muscle, in which case, numerous short fasciculi are attached to one or both sides of the tendinous cord, like the fibres of a feather to its stem, giving rise to the terms penniform, semi-penniform, and compound penniform, according to the arrangement. Examination of the Fibres.-Take a piece of boiled horseflesh (ordinary cat's meat) strip off a small portion of one of the fasciculi, place it in a drop of water on the slide, and teaze it well out, seeking to separate the fibres lengthwise, apply the covering glass, and examine under the low power. The object will resemble a bundle of sticks, with here and there a single one. Under the high power the fibres, with their transverse striæ, will be distinguished, and in some parts will be seen to be split up at their ends into fibrillæ. inch. In size the fibres vary but little, the average being Mr. Bowman finds the size, in the male, to be 32 inch, and in the female, 4. During the examination of the specimens of voluntary fibres, particularly from cooked flesh, a peculiar cleavage into discs will often be observed, as shown in the drawing (fig. 56). The appearance was recently noticed in beef that had been preserved for some months, nearly all the fibres showing the tendency to this transverse cleavage. The dark lines, or striæ, are 400 inch apart, and are particularly characteristic of voluntary muscle; but they nevertheless also exist in the muscular fibres of the heart, in the pharynx, and in the upper part of the œsophagus. Striated fibres do not anastomose nor divide, excepting in the heart, in the tongue of the frog, and in the facial muscles of some animals. Each fibre is invested by a transparent structureless membrane or sarcolemma, corresponding to the internal perimysium. Fig. 56. A. B. A. A muscular fibre, or primitive fasciculus, breaking up in the transverse In fishes the membrane, being tough and elastic, may easily be demonstrated, as it is often left entire when the substance of the fibre is torn across by being stretched. Fragments of an elementary fibre of the Skate, held together by the untorn but twisted sarcolemma. a. Sarcolemma. b, b. Opposite fragments of the fibre. A drop of acetic acid will render the nuclei of the sarcolemma apparent. In the fœtus they can be seen without the aid of chemical agents. Besides corpuscles like cells or nuclei lodged among the fibrils within the fibre, others exist between the fibres ('fusiform corpuscles,' Ellis), which correspond in aspect, and probably in function, with the corpuscles of connective tissue. In the muscles of the frog, Welcher discovered peculiar corpuscular bodies between the fibres, as depicted below. Portion of muscle of a frog, showing nucleated cells between the fibres. Examination of Fibrilla.-Among mammalia the pig furnishes the best examples of fibrilla, but their isolation is extremely difficult. They are more easily prepared from the insect. A good plan is to cut open the thorax of a fly, and remove a portion of the large yellow muscle which lines its walls; this should be teazed out in a drop of water on the slide, and covered with the thin glass as usual. A power of 400 to 800 diameters will be required to render the elements distinctly visible. Each fibril consists of a row of minute particles (sarcous elements) strung together like beads (fig. 59). When highly magnified these particles appear as dark squares with bright spaces between them; sometimes faint lines may be seen crossing the bright spaces. Under a still higher power the dark squares are seen to be somewhat constricted in the middle and surrounded by a bright area. The dark aspect of the central part probably arises from its refracting the light differently from the surrounding portions, as |