77] THE SK ULL OF A MI UR US— KINDRED 7 7 



sphenoid as typical of the cyprinoids and siluroids, basing his observations on 

 Silurus glanis and Cyprinus carpio. VroHk's figure of Silurus glanis also shows 

 a well developed alisphenoid. 



The developmental relations of the bone have been discussed above, but it 

 may be added that the roughened surfaces for the attachment of muscles and 

 ligaments of the adult is developed from the muscle fascia and connective tissue 

 surrounding the perichondrial lamella of the alisphenoid cartilage. 



The sphenotics. Next to the frontals, these are the most conspicuous paired 

 bones on the dorsal surface of the cranium (Fig. 10). Each is subquadrangular 

 in shape and has long interdigitating margins, projecting into the surrounding 

 bones. Anteriorly, each interdigitates with the posterior margin of the frontal, 

 the line between tliese two bones being continuous posteriorly with the sphenotic 

 -supraoccipital interdigitation. The posterior margin of the dorsal surface 

 of the bone extends in between the squamoso-pterotic and the posterior end 

 of the supra-occipital, almost touching the transverse crest of the latter. The 

 anterior lateral margin of the sphenotic is raised slightly, so that a dilitator 

 groove is formed along the latero-dorsal surface, for the insertion of part of the 

 dilitator operculi muscle and ligament. The surface of the bone is without 

 ridges and the lateral line canal ossification has sunken below the surface and is 

 invisible from above. The only foramina on the dorsal surface of the bone are 

 several for the passage of twigs of the ramus oticus of the facial. 



The lateral surface of the bone is grooved for articulation with the hyoman- 

 dibula (Fig. 20). This surface is ossified, but the face of the hyomandibula 

 which articulates with it, is still cartilage. The beginning of the ossification 

 in this region has been shown earlier (Figs. 19, 33). The articular facet is con- 

 tinuous posteriorly with a similar groove on the lateral face of the squamoso- 

 pterotic, and below it the two bones are separated from each other by a narrow 

 strip of cartilage, which extends ventrally as far as the prootic bone (Fig. 20). 

 The line of interdigitation between sphenotic and prootic extends antero-ven- 

 trally from the ventral end of this piece of cartilage and continues as far ante- 

 riorly as the dorso-posterior margin of the trigemino-facial foramen. From this 

 point as far forward as the mid-dorsal margin of the foramen the sphenotic 

 alone forms the margin. Here it comes in contact with the posterior end of the 

 alisphenoid and the suture between them extends dorso-ventrally as far as the 

 region where the sphenotic meets the frontal. Viewed from above the ventro- 

 extemal extent of the sphenotic is not very great. 



The internal surface of the bone forms an almost square area in the cranial 

 wall, from the dorsal margin of the trigemino-facial foramen to the supraoccipi- 

 tal (Fig. 7). Anteriorly it is in contact with the ahsphenoid in the margin of 

 the same foramen and above this with the frontal. The interdigitation with 

 the frontal continues posteriorly as the line between sphenotic and supraoccipi- 

 tal. Posteriorly the sphenotic meets the prootic and the continuation of this 

 suture to the supraoccipital is restricted by a small square of cartilage. A 



