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 
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 Fic. 16. From a section of the pyloric end 
(antrum pyloricum) of the stomach of the 
ends which provide for attach- rabbit: m.m., muscularis mucosae; t.m.c., 
circular layer of the muscular tunic; t.m.l., 
Meme mine attachme%¢nt-is effect="" qoneitadinal layer of the tuscular. tunic: 
edebyearstrons band? of fibrous). ‘ay Ce Snbmucosa, 
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 

