Abstract
AbstractBjerring, H. C. (Section of Palaeozoology, Swedish Museum of Natural History, Stockholm, Sweden). The nervus rarus in coelacanthiform phylogeny. Zool. Scripta 1(2): 57–68, 1972.–In the course of craniate vertebrate evolution the somatic motor portion of the second cranionerval segment probably became divided into two nerves, viz. the trochlear nerve and the rarus nerve. The rarus nerve, allied to the second‐metamere basicranial muscle, apparently migrated backwards from the middle to the posterior part of the evolving head. Devonian coelacanthiforms exhibit an endocranial passage indicating that the rarus nerve accompanied the glossopharyngeal nerve through the otic capsule; in contrast, in the Recent Latimeria, the corresponding nerve emerges from the endocranium somewhat further posteriorly in association with the vagus nerve. Within the evolutionary history of the coelacanthiforms, this backward displacement of the rarus nerve appears to be correlated with a progressive development of the second‐metamere basicranial muscle as well as with a number of changes in both the head skeleton and the brain.
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