Figure 305.— Mota mola: upper left, nasal 



region as seen externally: lower left, scales 



from upper middle region of body. 



of the columnar portion; articulates through cartilage 

 anteroventrally with the prootics and anterodorsally with 

 the exoccipitals. The posterior end of the parasphenoid 

 overlies the anterior half of the midventral surface of the 

 basioccipital and is held to it by fibrous tissue, the 

 basioccipital remaining largely cartilaginous in the re- 

 gion overlain by the parasphenoid. The anterodorsally 

 directed prongs of the basioccipital articulate by fibrous 

 tissue anteriorly with the exoccipitals and posteriorly 

 with the bifid neural spine of the first vertebra. The 

 medial edges of the anterodorsally directed prongs form 

 the lateral walls of the foramen magnum, while the dor- 

 sal wall is formed by cartilage and the ventral wall by the 

 dorsal surface of the columnar portion of the basiocci- 

 pital. The rim of the round concave posterior end of the 

 basioccipital articulates by fibrous tissue with the rim of 

 the concave anterior end of the first vertebra. 



Exoccipital. — A large, nearly flat plate; cartilage 

 filled along all of its edges of articulation with the other 

 cranial bones; articulates through cartilage dorsomedial 

 with the supraoccipital, dorsolaterally with the epiotic, 

 laterally with the sphenotic and pterotic, ventrally with 

 the prootic, and medially with the basioccipital. Along 

 the middle region of its medial edge the exoccipital ar- 

 ticulates by fibrous tissue with the anterodorsal prong of 

 the basioccipital. The exoccipital does not articulate 



with the first vertebra, nor does it enter into the forma- 

 tion of the walls of the foramen magnum. 



Supraoccipital. — A rounded plate ventrally, but 

 produced dorsally into a high and stout supraoccipital 

 crest; cartilage filled along all of its ventral edges; ar- 

 ticulates through cartilage laterally with the epiotics and 

 posteriorly with the exoccipitals. Anteriorly the base of 

 the supraoccipital is overlain by the frontals, with which 

 it articulates by fibrous tissue. 



Otic Region. 



Pterotic. — Broadly cartilage filled along its 

 anterior edge; articulates through cartilage antero- 

 laterally with the sphenotic, anteromedially on its dorsal 

 surface with the epiotic and exoccipital and antero- 

 medially on its ventral surface with the prootic. Along 

 most of the length of its dorsal surface the pterotic pos- 

 sesses an upraised flange just lateral to which the supra- 

 cleithrum articulates by fibrous tissue. Along most of the 

 length of its lateral surface a similar flange is present just 

 lateral to which the hyomandibular articulates by 

 fibrous tissue. 



Sphenotic. — Cartilage filled along its medial and 

 anterior edges; articulates through cartilage posteriorly 

 with the pterotic, dorsomedially with the epiotic and ex- 

 occipital, and ventromedially with the prootic and 

 pterosphenoid. Anteriorly the sphenotic articulates by 

 fibrous tissue with the overlying frontal. At its postero- 

 dorsal edge the sphenotic possesses a posterior process 

 which articulates closely by fibrous tissue with the dorsal 

 surface of the pterotic and which supports the antero- 

 medial edge of the supracleithrum. Posteriorly along its 

 ventral surface the sphenotic articulates by fibrous tissue 

 with the anterior edge of the hyomandibular. 



Epiotic. — A more or less rounded plate ventrally, 

 but prolonged posterodorsally into a spine which con- 

 nects by a tendon to the muscle mass of the dorsal fin; 

 cartilage filled along all of its ventral edges; articulates 

 through cartilage medially with the supraoccipital, pos- 

 teriorly with the exoccipital and laterally with the 

 sphenotic. Anteriorly the epiotic articulates by fibrous 

 tissue with the overlying frontal. 



Prootic. — Cartilage filled along all of its edges of 

 articulation with the other cranial bones; articulates 

 through cartilage anterodorsally with the pterosphenoid, 

 anterolaterally with the sphenotic, posterolaterally with 

 the pterotic, and posteriorly with the exoccipital and 

 basioccipital. The anteroventral edge of the prootic ar- 

 ticulates by fibrous tissue with the posterodorsal wing of 

 the parasphenoid, while more posteriorly the medial edge 

 of the prootic similarly articulates with the lateral edge 

 of the parasphenoid. Along its anteroventral edge the 

 prootic is produced into a laterally expanded wing which 

 articulates by fibrous tissue with the anteromedial edge 

 of the dorsal end of the hyomandibular. 



