85] THE SKULL OF AM I URUS— KINDRED 85 



prong of the post-temporal bone is firmly fastened by ligament to the posterior 

 surface. A ligament of the trapezius muscle is attached to the crest below the 

 post-temporal. The crest itself continues medially on the supraoccipital. 



At first sight this part of the bone appears as an isolated element, because 

 the squamoso-pterotic bone extends in beneath the crest, and apparently 

 separates this part of the bone from the more posterior portion. Closer 

 inspection shows that the crested part of the bone and the more posterior part 

 are a continuum, although the latter is rugose and concave just behind the crest, 

 giving the unpression that the crested part of the bone is a separate piece. 

 The posterior part of the bone slopes ventrally to form part of the posterior sur- 

 face of the cranium (Fig. 9). Medially it is separated from the supraoccipital 

 by a strip of cartilage which continues around the ventral margin of the bone, 

 there separating it from the exoccipital. Above this, on the lateral surface of 

 the cranium it interdigitates with the pterotic part of the squamoso-pterotic. 

 This portion of the epiotic is thin and concave ventrally for the insertion of 

 fibres of the adductor operculi muscle. It does not develop from the perichon- 

 drium of the otic capsule, but by ossification of connective tissue around the 

 ends of the muscle fascia. 



The posterior surface of the bone is corrugated for the insertion of the ends 

 of the trapezius muscle fibres. Thus the external surface of the epiotic bone is 

 covered with a superficial ossification developed from muscle fascia, which 

 covers most of the outer perichondrial lamella. 



The internal surface of the bone forms the posterior and dorsal walls of 

 the recess for the posterior semicircular canal. Most of the wall is completely 

 ossified and the cartilage has been resorbed except along the margins of the bone. 

 In the earlier stages this part of the otic capsule had an inner lamella which was 

 connected across the walls of the recess by osseous trabeculae (Fig. 38), and 

 which now forms the solid central part of the posterior wall of the recess. 



Although it has been definitely demonstrated by Huxley, Parker, Schleip 

 and Gaupp, that the epiotic bone of the teleosts is a distinct otic ossification 

 developed from the posterior dorsal part of the otic capsule waU, the Cuverian 

 name 'occipitale externum' is still prevalent in the literature. Sagemehl (1884) 

 modified the term and called it the 'exoccipitale' in his work on Amia, the 

 Characinidae and the Cyprinidae. Allis followed him and in all except his most 

 recent papers has named it according to Sagemehl, although this introduces 

 confusion with the true exoccipitals. 



In all of the teleosts this bone lies at the posterior dorsal angle of the cranium 

 as in Amiurus, and bears more or less of a crest for articulation with the post- 

 temporal part of the shoulder girdle. Sometimes the epiotic is limited more to 

 the dorsal surface of the posterior region of the otic capsule, but usually a part 

 of it extends ventrally as the hinder wall of the posterior semicircular canal. 

 Its homologies are evident throughout the teleosts and even in most ganoids 

 it is a well developed ossification. 



