T, he culmination of more than a half century of research in frog muscle was the demonstration of the existence in that species of a separate and distinct slow or tonic striated muscle system that possessed its own peripheral nerve supply and motor units. Thus, the frog has two distinct contractile systems which have different biological functions: a fast or tetanic striate muscle system and a ...

Genetic regulatory networks governing skeletal myogenesis in the body are well understood, yet their hierarchical relationships in the head remain unresolved. We show that either Myf5 or Mrf4 is necessary for initiating extraocular myogenesis. Whereas Mrf4 is dispensable for pharyngeal muscle progenitor fate, Tbx1 and Myf5 act synergistically for governing myogenesis in this location. As in the...

The morphological and physiological classification of the fibres of the extraocular muscles has been the subject of some controversy, not to say confusion. It is well known that in mammals the oblique and rectus muscles consist of a peripheral layer of smaller fibres overlying a deeper zone with larger diameters (Kato, I938; Kern, I965). Many morphological and ultrastructural studies have descr...

The saccadic system accurately compensates for perturbations of eye position produced by microstimulation of the superior colliculus. This requires that information about the stimulation-induced change in eye position be provided by an extraretinal source--either proprioceptive endings in extraocular muscles or a centrally generated corollary discharge. It is shown that compensation remains int...

To the Editors: Ocular motility problems related to congenital abnormalities of the extraocular muscles are rare. Such congenital abnormalities may present in a spectrum from accessory additional rectus muscles to the absence of extraocular muscles.1-5 Absence of one or more extraocular muscles is a rare condition usually seen in association with craniofacial syndromes. We present a case of bil...