252 W. M. Baldwin 



fibrillae is well nigh impossible with our present optical Instruments. 

 When viewed in such vertical planes it appears as if those tendon 

 fibrillae terminating in the sarcolemraa indentations were really 

 within the muscle fibre. Undoubtedly a neglect to take into con- 

 sideration these facts has led to several erroneous conclusions such 

 as are represented iu various published figures. Accordingly, I have 

 preferied to base my conclusions upon a careful study of those fibrillae 

 which occupy the same horizontal optical plane. Under such circum- 

 stances the sarcolerama presents an unbroken contour. No evidence 

 can be found bespeaking a continuity of tendon fibril with muscle 

 fibril among these various extrinsic eye muscles of the white mouse, 

 gray raouse, chicken, or calf. 



One of the best bits of evidence upon this question is furnished 

 by muscles of the bipenniform type. I have represented in fig. 4 

 a portion of a Single muscle fibre of this type of an adult white 

 mouse with its attached central tendon. As is readily seen the 

 tendon fibrillae [Ä] lie at an angle of about 125° with the muscle 

 fibrillae (C). The sarcolemma investing the fibre is considerably 

 thickened at that end applied to the tendon. The numerous muscle 

 fibrillae are represented half-schematically but their relation to this 

 sarcolemma end is faithfuUy reproduced. Between the sarcolemma 

 and the tendon there are to be seen several layers of connective 

 tissue fibres and cells (B). I was able by means of various methods 

 of hematoxylin staining to stain at once these three structures, 

 central tendon, intervening connective tissue, and muscle fibrillae 

 three different colors upon the same slide. The tendon fibrillae 

 were yellowish-white, the connective tissue (peritendinum) reddish- 

 brown, and the muscle fibrillae deep brown. There was absolutely 

 no structural coutiuuity to be seen between either the tendon fibrillae 

 and the connective tissue fibrillae or between the latter and the 

 muscle fibrillae. At no place could it be demonstrated that the muscle 

 fibrillae traversed the connective tissue sheath in order to reach 

 the central tendon, nor did they perforate the sarc.olemma and turn 

 at an angle to join the connective tissue fibrillae. 



In muscles belonging to this type of structure the relation of 

 the muscle fibres to the tendon is precisely similar to that of those 

 muscles which are attached to bones, to the bone upon which they 

 find their Insertion. Such muscle fibres have only an indirect rela- 

 tion to the bone siuce their actual attachment is direct to the peri- 

 osteum. Such is the case with these bipenniform muscles. Only 



