FORM AND ATTACHMENT OF MUSCLES 



357 



these that during contractions of the muscle the blood passes to relieve the tension in the longi- 

 tudinal capillaries. 



Veins accompany the arteries, and even the ynaller ones possess valves (Spalteholz). 



The nerve endings in voluntary muscle comprise both motor and sensor varieties. A motor 

 nerve pierces the epimysium and breaks up into numerous branches to form an interfascicular 

 plexus in the perimysium. From this plexus nerve fibrils arise, and usually one nerve fibril passes 

 t > each muscle fibre. The nerve fibril pierces the sarcolemma, the neurilemma, and myelinic 

 sheath disappearing before the nerve fibril reaches the muscle fibre, and probably being lost 

 by fusing with the sarcolemma. The naked axone beneath 

 the sarcolemma of a fibre continues to the surface of the 

 muscle fibre and undergoes arborization to form an end oryan. 

 Around the end organ is a quantity of granular sarcoplasm, 

 which, with the nerve and organ, constitutes a sole plate. 

 A sensor nerve takes origin from a muscle spindle, which 

 consists of a bundle of encapsulated muscle fibres about sensor 

 nerve twigs. 



Involuntary striated or cardiac muscle is found in the 

 heart and is not under the control of the will. Each fibre is 

 a short cylinder varying from 100/z to 200^ in length and 

 of about 25 fi to 40 fj. in diameter. The striations are both 

 longitudinal and transverse, but the latter are usually not 

 distinct. Each fibre is surrounded by a delicate membrane. 

 The cells give off narrow processes of branches which con- 

 nect with each other, thus forming "a reticulum of muscle 

 fibres. The meshes of this reticulum are occupied by areolar 

 tissue in which the vascular and nerve supply of the tissue 

 is situated." 



Usually a single, large, oval nucleus occupies the centre of 

 the cell and is surrounded by an area of clear and undiffer- 

 entiated protoplasm in which fibrillse do not exist. Pigment 

 granules are seen in this undifferentiated protoplasm. 



Purkinje fibres are peculiar muscle fibres found in the 

 heart, and will be described with that organ. 



The nerves are both sympathetic and cerebrospinal. 



Involuntary non-striated or smooth muscle is not under the control of the will. It is found 

 in the alimentary tract from the middle third of the oesophagus down, in gland ducts, trachea, 

 bronchi, bronchial tubes, in the urinogenital system, bloodvessels and lymph vessels, etc. It is 

 found arranged in layers that encircle the organs longitudinally, transversely, and sometimes 

 in an interlaced manner. 



FIG. 284. Anastomosing muscle 

 fibres of the heart, seen in a longitu- 

 dinal section. On the right the limits 

 of the separate cells with their nuclei 

 are exhibited somewhat diagrammat- 

 ically. 



Nuclens- 



Intercettular 



bridges' 



FIG. 285. Longitudinal section in the smooth muscle of a dog's large intestine, to show especially intercellular 

 bridges. X 530. (Szymonowiez and MacCallum.) 



Each fibre is short and spindle-shaped, varying from 25 n to 200 ft in length and from 5 /z 

 to 7 fj. in diameter. In the gravid uterus they are much larger in both dimensions. Occa- 

 sionally, longitudinal striations are seen, and then the fibrillse so formed are coarse and periph- 

 erally located. Each fibre contains a single slender nucleus which is centrally located. Branched 

 fibres are occasionally seen in the aorta and in the bladder. 



The bloodvessels form a meshwork between the fibres. 



The nerves are from the sympathetic system, though Kuntz has recently shown that in some 

 organs, at least, the nerves are originally derived from the vagus. 



Form and Attachment of Muscles. The muscles are connected with the bones, 

 cartilages, ligaments, and skin, either directly or through the intervention of 

 fibrous structures called tendons or aponeuroses. Where a muscle is attached 

 to bone or cartilage, the fibres terminate in blunt extremities upon the periosteum 



