8 1 ] THE SKULL OF A MI UR US— KINDRED 81 



the dorsal part of the lateral wall of each recessus sacculi the posterior margin 

 of the prootic is sutured to the exoccipital. This suture continues laterally in 

 the labyrinth recess as far as the base of the lateral septum semicircularis. The 

 bulk of this septum persists as cartilage and separates the lateral margin of the 

 prootic from the exoccipital. A lamella of the prootic extends up on the ante- 

 rior face of the cartilage and its dorsal end is separated from the posterior ventral 

 margin of pterotic part of the squamoso-pterotic and the inner lamella of the 

 supraoccipital by cartilage. Anteriorly, in the floor of the lateral recess, the 

 prootic meets the pterotic and the line between them extends anteriorly as far 

 as the outer end of the anterior septum (Fig. 7). This septum is also partly 

 cartilage, and the prootic lamella embraces its ventral surface and is confluent 

 with the inner surface of the wall of the anterior recess, formed by a vertical 

 projection from the floor of the prootic. In the younger stage this wall was 

 cartilage and showed the beginnings of perichondria! ossification on both its 

 cerebral and labyrinthine surfaces. The cartilage at the cerebral end of the 

 septum anterius separates the prootic lamella from the supraoccipital. 



I have not been able to find the eye-muscle canal which McMurrich (1884b) 

 described as occurring between the prootic, parasphenoid and basioccipital. 

 These bones are very tightly pressed together in this region and there is no 

 space between them. 



Cuvier (1826) first described this bone in the fishes as the homologue of 

 the human ala magna. About the same time Meckel (1824) recognized it as the 

 homologue of the petrosal because of its relation to the labyrinth and the facial 

 nerve. His ideas were further elaborated by Hal'mann (1837), who revised the 

 nomenclature of the bones in this region, but retained this name. Stannius 

 (1853) called it the ala temporahs because of its general similarity to the tem- 

 poralis of the mammals. As is well known Huxley (1864) homologized this bone 

 in Esox with one of the three ossification centers of the petrosal part of the 

 temporalis of man and called it the prootic. Some of the modern authors have, 

 nevertheless, retained the term petrosal, although on comparison with the 

 petrosal of mammals it can be compared only to the part defined by Huxley. 



The prootic is one of the constant bones of tlie piscine cranium and usually 

 has the same general relations to the anterior semicircular canal and the facial 

 nen^e. In those teleosts which have an eye-muscle canal (Salmo, Scomber, the 

 Loricati, etc.) the facialis issues through the bone, separate from the trigeminus. 

 In groups in which the eye-muscle canal is not developed, as in Amiurus, the 

 facialis issues through a notch in the anterior edge of the prootic. In most 

 forms, whether an eye-muscle canal be present or not, the median ventral ends 

 of the bones of the two sides are fused in the floor of the cranium. The eye- 

 muscle canal usually lies ventral to the median ends of these bones, which form 

 its roof. The parasphenoid in such cases forms the floor and part of the side 

 walls of the canal. The presence of a large amount of cartilage within the bone 

 has been remarked in Scomber and the Loricati (Allis), and in some of the 



