236 MUSCLES AND FASCIA. 



rod-shaped nucleus, which sometimes appears as a narrow, continuous, dark streak. 

 The fibres are united into bundles, which are connected together by areolar tissue 

 and elastic fibres. This form of muscular tissue occurs either scattered' in the 

 areolar tissue, or exists in the form of a muscular membrane, the bundles being 

 arranged parallel, or forming a close interlacement, crossing each other at various 

 angles. The muscular fibre of organic life is found in the alimentary canal, form- 

 ing the muscular coat of the digestive tube from the middle of the oesophagus to 

 the internal sphincter of the anus ; in the posterior wall of the trachea, and in the 

 bronchi; in the ducts of the submaxillary glands; in the gall-bladder and common 

 bile duct ; in the calyces and pelvis of the kidney ; in the ureters and bladder ; 

 and, scantily, in the urethra. In the female it is met with in the vagina, the 

 uterus, Fallopian tubes, and broad ligaments ; in the male, in the scrotum, the epi- 

 didymis, the vas deferens, vesicula3 seminales, the prostate ; and in the cavernous 

 bodies, in both sexes. It is found also in the coats of all arteries, in most veins, 

 and lymphatic vessels ; in the iris and ciliary muscle, and in the skin. 



Bloodvessels are distributed in considerable abundance to the muscular tissue. 

 In the voluntary muscles the capillaries, which are of extremely minute size, 

 form narrow, oblong meshes, which run in the direction of the fibres. 



The lymphatic vessels in muscles are few in number, and appear to exist only 

 in the largest muscles. The nerves of voluntary muscles are of large size. The 

 larger branches pass between the fasciculi, and, subdividing, unite to form primary 

 plexuses ; from these, finer bundles, or, single nerve tubes, pass between the mus- 

 cular fibres, and, forming loops, return to the plexus. 



Each muscle is invested externally by a thin cellular layer, forming what is 

 called its sheath, which not only covers its outer surface, but penetrates into its 

 interior in the intervals between the fasciculi, surrounding these, and serving as 

 a bond of connection between them. 



The muscles are connected with the bones, cartilages, ligaments and skin, either 

 directly or through the intervention of fibrous structures, called tendons or apo- 

 neuroses. Where a muscle is attached to bone or cartilage, the fibres terminate 

 in blunt extremities upon the periosteum or perichondrium, and do not come into 

 direct relation with the osseous or cartilaginous tissue. Where muscles are con- 

 nected with the skin, they either lie as a flattened layer beneath it, or are con- 

 nected with its areolar tissue by larger or smaller bundles of fibres, as in the 

 muscles of the face. 



The muscles vary considerably in their form. In the limbs, they are of con- 

 siderable length, especially the more superficial ones, the deep ones being generally 

 broad ; they surround the bones, and form an important protection to the various 

 joints. In the trunk, they are broad, flattened, and expanded, forming the parietes 

 of the cavities which they inclose ; hence the reason of the terms, long, broad, 

 short, etc., used in the description of a muscle. 



There is considerable variation in the arrangement of the fibres of certain 

 muscles, to the tendons to which they are attached. In some, the fibres are 

 arranged longitudinally, and terminate at either end in a narrow tendon. If the 

 fibres converge, like the plumes of a pen, to one side of a tendon, which runs the 

 entire length of a muscle, it is said to be penniform, as the Peronei ; or, if they 

 converge to both sides of a tendon, they are called bipenniform, as the Rectus 

 femoris ; if they converge from a broad surface to a narrow tendinous point, they 

 are then said to be radiated, as the Temporal and Glutei muscles. ' 



Their size presents considerable variation ; the Gastrocnemius forms the chief 

 bulk of the back of the leg, and the fibres of the Sartorius are nearly two feet in 

 length, whilst the Stapedius, a small muscle of the internal ear, weighs about a 

 grain, and its fibres are not mpre than two lines in length. 3~n each case, how- 

 ever, they are admirably adapted to execute the various movements they are 

 required to perform. 



The names applied to the various muscles have been derived : 1, from their situa- 

 tion, as the Tibialis, Badialis, Ulnaris, Peroneus ; 2, from their direction, as the 



