226 The Miceoscope. 



Several English sparrows were also studied, while only one shrew 

 and two bats were examined.* The longest muscle found in these 

 animals, the latissimus of a field mouse, was 27 mm. long, which is 

 less than 30 mm., the number mentioned by Kolliker and usually 

 accepted as the lowest limit of a fiber in a long muscle from any of 

 the larger animals. 



In general form the fibers of the trunk and limb muscles of 

 these small animals are of three kinds — cylindrical, tapering and 

 fusiform. Their arrangement is diagrammatically shown in Plate I., 

 Figs. 1 to 9. 



1. Cylindkical Fibeks — Are those which extend from tendon 

 to tendon of the muscle with a nearly uniform diameter (Fig. 1). In 

 the shorter muscles these were the only kind found. f This was 

 found to be the case in the intercostals (3 J to 4 mm.), the short 

 muscles of the back (5 mm.) and the diaphragm (4 mm.) of the 

 mouse and bat ; the penniform muscles from both cephalic and 

 caudal limbs of the mouse, bat and sparrow (the fibers varying in 

 different muscles and in different parts of the same muscle from 1 

 to 7 mm.), and in the rectus abdominis of the mouse, a poly gastric 

 muscle, the sections between the raphes being 4 to 5 mm. 



One of the longer muscles (10 mm,) from the shoulder of a 

 mouse seemed also to be composed entirely of fibers which extend 

 from tendon to tendon, while in the latissimus (25 to 27 mm.) of the 

 mouse no fibers were traced the full length of the muscle. In some 

 of the longer muscles the majority of the fibers extend from tendon 

 to tendon, as in the rectus capitis (9 mm.) of the mouse. In others 

 only occasionally could a fiber be traced from one end of the muscle 

 to the other. This was done in the vastus externus of the mouse, a 

 muscle varying in different specimens from 16 to 22 mm., and in the 

 same muscle (9 mm.) of the bat, the shrew (8 mm.) and the English 

 sparrow (14 mm.); in the pectoral (18 mm.), the trapezius (15 mm.) 

 and the obliquus abdominis (14 mm.) of the mouse; in the rhomboid 

 of the English sparrow and the obliquus abdominis of the bat. 

 While there seem to be few cylindrical fibers in these longer 

 muscles, their apparent rarity may be partially due to the difficulty 

 of isolating them sufficiently to trace them. 



2. Tapering Fibers — Are those having one termination large 

 and more or less blunt at one tendinous attachment of the muscle. 



* The species studied were the house mouse (Mus musculus [Linn] ), both younp and 

 adult, the flekl mouse (H«sperom!/sJettcopws [Raf] )■ adult, the mole shrew (fitortna 6revt- 

 cauda [Say]), the bi-own ha,t{Vespertilio subulatus [Sav] ), the gray bat {Atalapha cinereus 

 [Beauv.]), and the English sparrow (Patser domesticus [Linn] ), both young and adult. 



t For convenience the muscles may be classified as shorter, those 7 mm. and less 

 between the tendons, and longer, those 8 mm. and over. 



