126 ALAN C. SUTTON 



the appearance of striations. As soon as the striations appeared 

 there could be no further trouble. 



In the development of the eye muscle (Lewis) the premuscle 

 mass is first detected in the 7 mm. human embryo. At this 

 stage the third cranial (oculomotor) ner\'e enters the anterior end 

 of the premuscle mass, dorsal to the optic stalk. At 9 mm. the 

 muscle mass is somewhat enlarged. It begins to split into the 

 different muscles, each with its respective nerve. The oculo- 

 motor, trochlear and abducens nerves have all now entered the 

 muscle, which as yet is not attached either to sclera or to the pre- 

 cartilage but is still directly continuous with the mesenchyme. 

 At 11 mm. the muscle is to be found dorsal and caudal to the 

 optic stalk and mostly medial to the ej^eball, partly continuous 

 with the primitive sclera and "with the precartilage about the 

 optic nerve. At 14 mm. all the orbital muscles can be distin- 

 guished and have nearly the adult relations to the bulbus oculi. 

 The early development is identical in both the human and earl}^ 

 pig embryos. 



So far, the muscles are composed entirely of myoblasts with 

 no definite muscle bundles (Bardeen '00). At 18 mm. some of the 

 cells have passed from the round myoblast state to the spindle- 

 shaped muscle cell, in which the myofibrils begin to be laid down. 

 At the 26 mm. stage, the entire periphery of the cell is filled 

 with the striated myofibrils. Here some of the cells are now of 

 muscle fiber type — very long spindle cells. These are divided 

 into bundles with the older fibers centrally arranged. From now 

 on the individual fibers increase in length and thickness, fibrils 

 fill the fiber and are added peripherally. At 120 to 130 mm. the 

 muscle nucleus, which up to this time was centrally located, 

 comes to Ue at the periphery of the fiber. By the 180 mm. stage 

 all the nuclei are at the periphery and the sarcolemma has be- 

 come distinct. Striated fibers are not produced after the first 

 half of embryonic Ufe in the human (Macallum '98) and only for 

 a short time after birth in the pig (Bardeen). Many of the 

 fibers first formed degenerate during embryonic life — perhaps 

 because they fail to form a union with a nerve fiber; I have 

 never found a degenerating fiber with a nerve ending. 



