390 Dr. Otto 31. Em — Structure of Squaloraja and Chimcera. 



the contours of superficial structures appended to the cranium are 

 frequently determined in the main by the shape of the fundamental 

 cartilage to which they are attached." The application of this 

 principle is well exhibited in the vasodentine dermal skeleton of 

 Elasmobi'anchs in general, v/hen there is no direct attachment or 

 relationship to the muscles. But the illustration of the frontal 

 spine is especially interesting. It is long when adapted to a long 

 and strong rostrum (Squaloraja and Mtjriacanthus) , short when 

 adapted to a weak or reduced rostrum (Iscliyodus and Chimcera) ; 

 laterally compressed when on a laterally-compressed rostrum, verti- 

 cally compressed when on a skull like that of Squaloraja. 



EXPLANATION OF PLATE. 



Fig. 1. — Squaloraja polyspondtjla, A,o^ass. : median rostral cartilage, probably of 

 female, from above (a) and in transverse section at proximal end {b). 

 cr. fragments of cranium ; I. fibrochondral lamellfe. [British Museum.] 



Fig. 2. — Ditto : transverse section of frontal spine, enlarged about 80 diameters, 

 showing enclosed cells and blood-vessels, the upper edge representing the 

 inner border resting against the soft cartilaginous axis. 



Fig. 3. — Chimceropsis paradoxa, Zittel: cranium of female, about one-sixth nat. 

 size ; contour restored in dotted lines. [Paleeontological Museum, 

 Munich.] 



Fig. 4. — Squaloraja polyspondyla, Agass. : frontal spine, inferior aspect, showing 

 grooves for adductor muscles. 



Fig. 5. — Ditto : transverse sections of spine, showing inner cavity and the bilaterally 

 symmetrical arrangement of blood-vessels. 



Fig. 6. — Ditto : dorsal aspect of head, restored after figures by Agassiz, "W". 

 Davies, and A. S. Woodward, a, b, calcified rings of '"'lateral line"; 

 I, Ha, lie, labial cartilages ; Ei, median roatral cartilage ; E^, lateral 

 ditto. 



Fig. 7. — ChAmmra monstrosa, Linn. : right half of anterior side of mouth and nasal 

 opening, from below. The corner of the mouth and lip are raised to 

 show arrangement of labial cartilages, and the arrow divides the labial 

 complex into that of the upper and that of the lower lip. 



Fig. 8. — Ditto: right side of head of male, a little from above, the skin removed 

 as far as the eye, and displaying the lens {I.), iris («r.), and the deep 

 cutaneous or sclerotic fold {x.) round the iris. The dotted surface indicates 

 the rostral, cranial, labial, and mandibular cartilages. The tendon {t.) 

 of the hinder attachment of the frontal spine connecting it with the 

 cranial roof above the orbit is unshaded on the right side, and indicated 

 by z^i on the left side. The uppermost and hindermost fibres of the 

 adductor mandibularis are attached to these tendons and to the broad 

 inferior surface of the frontal spine itself (/.«.). The tendons of the 

 levator anguli oris {l.a.o.) are attached on the upper anterior surface of 

 the base of the spine. The tendons proceeding from the internasal cranial 

 crest and the median rostrum itself (Ej) are the ligamental supports of 

 the rostral sensory apparatus : the right lateral rostral cartilage (E^) is 

 ' seen in front of the nasal capsule («.). 



Fig. 9. — Ilenaspis armata, Ewald : left half of cranium and anterior portion of 

 trunk, from above (after Jaekel), showing the probably male parietal 

 horn-like (? chondrodermal) appendages {jihi, joAn, ph\\\) ^'^^ the true 

 dentodermal lateral spine {l.i.) corresponding in form, attachment, and 

 superficial ornamentation to the armature of the trunk, but differing 

 in these and other macroscopical characters from the appendages ph., 

 probably chondrodermal calcifications like the frontal appendages of 

 Chimcera, Myriacanthus, and Squaloraja (Figs. 6, 8, 11). 



Fig. 10. — Chimera monstrosa, Linn. : arrangement of "lateral line" in respect to 

 the cranial, labial, and rostral cartilages below {cf. Fig. 6, Squaloraja). 



Fig. 11. — Myriacanthus granulatus, Egert. : frontal spine showing lateral muscular 

 grooves on proximal end. cr. cranium ; Ej, median rostral prolongation. 



