Muscular Tissues. 



35 



The muscular substance of the heart differs both from striated 

 and smooth muscle in being composed of branched anastomosing 

 fibres, which apparently form a continuous network. Like striated 

 muscle, it possesses characteristic transverse markings, but, like 

 involuntary muscle, it is under the control of the sympathetic 

 nervous system. 



As gross structures the voluntary muscles are functional units, 

 each of which has a particular action according to the movement 

 permitted by the parts of the skeleton to which it is attached. 

 They present a longitudinal striation which is roughly referred to as 

 the direction of the fibres, and which is of great value in identifi- 

 cation. The striation is due to 



t.tns. 



. rn.m. 



the circumstance that the fibres 

 are arranged in parallel groups 

 or muscle bundles, each of which 

 is surrounded and separated 

 from the adjacent bundles by a 

 connective tissue enclosure, the 

 perimysium. 



A muscle is typically spindle 

 shaped, consisting of a middle 

 fleshy portion, termed the belly 

 of the muscle, and of tapering 

 ends which provide for attach- 

 ment. The attachment is effect- 

 ed by a strong band of fibrous 

 connective tissue, the muscle 



tendon (Figs. 7, 34). Some muscles, such as those of the abdominal 

 wall, are disposed in the form of flattened sheets, the ends of which 

 are attached by broad, thin sheets of connective tissue, the apon- 

 euroses. In unipennate muscles the fibres are attached obliquely 

 to the side of the tendon, or in bipennate muscles to both sides, 

 like the vane of a feather. In the so-called biceps, triceps and 

 quadriceps muscles of the limbs, the origin is divided into two, 

 three or four portions. The recognition of origin and insertion 

 (p. 63) depends on usual but not invariable relations. The exact 

 effect of muscle contraction depends as a rule on the relative 

 positions of the parts and on the synchronous action of other 

 muscles. A muscle like that forming the diaphragm does not 



Fig. 16. From a section of the pyloric end 

 (antrum pyloricum) of the stomach of the 

 rabbit: m.m,, muscularis mucosae; t.m.c, 

 circular layer of the muscular tunic; t.m.l., 

 longitudinal layer of the muscular tunic; 

 t.ms., mucous tunic; t.s., tela submucosa; 

 t.sr., serous tunic. 



