78 ILLINOIS BIOLOGICAL MONOGRAPHS [78 



shallow recess about in the center of the cerebral surface of the sphenotic con- 

 tams the cerebral end of a canal through which the ramus oticus facialis passes 

 and which emerges by several foramina on the dorsal surface as already mentioned. 

 The anterior end of the recess for the anterior semicircular canal lies within the 

 bone, but the canal itself does not extend to the end of the recess. The 

 internal surface of the recess, noted above as filled with trabeculae (Figs. 2)3, 36), 

 has now entirely ossified so that this part of the sphenotic bone is sohd. Carti- 

 lage between the inner and outer lamellae of the bone has not been entirely 

 replaced, traces of it occurring between the pterotic and the sphenotic. The 

 large cartilaginous roof present in the 32 mm. stage between the supraoccipital 

 and the medial dorsal edge of the sphenotic (Fig. 3) has been covered by peri- 

 chondrial ossification continuous with the latter. The lateral line ossification 

 has become an integral part of the bone, although restricted to a very small area 

 (Fig. 11). There are no sense organs within the lateral hne canal in the spheno- 

 tic nor are there any tubules leading to the exterior. 



From Cuvier (1826) to Parker (1872), the sphenotic was regarded as the 

 homologue of the postfrontal of the reptiles, and so named. Parker first called 

 it the sphenotic and described it in Salmo as an ectosteal ossification of the otic 

 capsule above the ampulla of the anterior semicircular canal, thus grouping it 

 with the other otic bones described by Huxley (1864). Up to that time the 

 criterion for the homology of this bone was based upon morphological rather 

 than ontogenetical relations. Vrolik (1872) devotes a short paragraph to the 

 names which this bone has borne in the older literature, but calls it the post- 

 frontal and describes it in the teleosts as a 'perichondrostische ossifikation,' 

 the equivalent of a dermal bone of the present paper. In Amia (Bridge, 1877; 

 Sagemehl, 1884) the bone was called the postfrontal, until AUis (1898) revised 

 the nomenclature of the problematical bones of this animal, and called it the 

 postorbital ossification. The use of this term was unfortunate because he had 

 already applied the name postorbital to a bone of the infraorbital series as the 

 homologue of the reptilian postorbital. The name postfrontal was given to the 

 superior dorsal bone of the infraorbital chain and from his definition of it, I have 

 followed him in naming its homologue in Amiurus. In Scomber (AlUs, 1903), 

 he uses the same confusing terms, postorbital bone and postorbital ossification 

 for postorbital and sphenotic respectively, justifying his terminolog>', on the 

 basis, that they should not convey any relationship to the bones of the higher 

 groups. The term sphenotic as used by Parker is more expressive of the devel- 

 opmental relations of this bone than the terminology of Allis and, as this bone 

 is strictly a piscine and avian ossification, no confusion will arise through its 

 use. Allis (1910) evidently has changed his views and has called the homolo- 

 gous bone of the Loricati, the sphenotic. 



Ridewood (1904) maintains that the term postfrontal should be retained 

 because it describes the uppennost surface of the bone, the lateral line element. 

 According to Allis (1898) the postfrontal never fuses with an underlying peri- 



