330 PEOF. T. W. BKIDG-E ON THE MOEPHOLOGT OE THE SKULL 



portion of the palato-pterygoid bone (figs. 1 and 2, p.pt.a'.), and to this process, as 

 well as to the fibrous connection between the dermal ethmoid and the fronto-parietal, 

 the anterior portion of the bone is firmly connected by ligamentous fibres. The 

 extremity of the outer division of the fork approaches closely to the posterior margin 

 of the cartilaginous olfactory capsule, but does not in any way contribute to the 

 formation of a hinder Avail to the capsule. Posteriorly, the bones contract to the 

 condition of slender, laterally-compressed rods, and at the same time become widely 

 separated from each other, eventually terminating behind in pointed extremities. 



The identification of these bones, which are present in all existing Dipnoi, and have, 

 on the whole, similar relations to other cranial structures as already described for 

 Lepidosiren, has given rise to much divergence, of opinion. Bischoff (I. c.) termed 

 them "jugal " bones (" Jochbeine"? "), although it is evident that he entertained some 

 doubt as to the accuracy of his interpretation. By Hyrtl (I. c.) they were named super- 

 ciliary bones (" Superciliarknochen "). In Protopterus the homologous structures have 

 been termed " Frontale, inch Frontale post " (Peters, I. c), " frontals " (Cobbold, I. <?.), 

 "super-temporal" (Owen, I. c), "supraorbital" (Huxley, I. c), "tendon-bones" 

 (" Sehnenbeine," Wiedersheim, I. c), and in Ceratoclus " os frontale " (Giinther, I. c), 

 " frontal," Miall (/. <?.), and " inner lateral bones," but probably representing the 

 frontals of Polypterus (Huxley, I. c). The term " jugal " is obviously inappropriate, 

 as Cobbold pointed out, and " superciliary " or " supraorbital " are purely descriptive 

 names based on the relation of the anterior portion of each bone to the orbital cavity. 

 It is also clear that the bones in question have nothing in common with the bones 

 ordinarily termed " frontals " in other Fishes, inasmuch as, except at their anterior 

 extremities, they are widely separated from the proper cranial roof by the whole thick- 

 ness powerful jaw-muscles, and lie directly beneath the dermis and scales of the super- 

 ficial skin. On the other hand, the term " Sehnenbein," applied by Wiedersheim to 

 the essentially similar bone in Protopterus, is somewhat novel, and on this point his 

 own words may be quoted. After referring to the position of the two bones dorsad 

 to the proper cranial roof, Wiedersheim says : — " Am frischen Praparat ist der 

 ganze Zwischenraum von dem zum Processus coronoideus mandibulse ziehenden 

 M. temporalis ausgefullt, und mit der gewaltigen Entwickelung des genannten Kau- 

 muskels bringe ich auch die Entstehung der beiden sonderbaren Knochenlamellen 

 in Verbindung, d. h. ich halte sie fur in Folge des Muskelzuges entstandene Ossifica- 

 tionszonen in der Fascia temporalis resp. in der fast den ganzen Kopf einhiillenden 

 subcutaneus Fascia; uberhaupt. Mit dem bis jetzt dafiir gebrauchten Namen ' Supra- 

 orbitalknochen ' ist nichts erklart, ja der Name is schon deswegen nicht passend, weil 

 sie sich weit fiber das Gebiet der Augenhohle hinaus erstrecken " (I. c. pp. 46-47). 

 According to Wiedersheim, therefore, the bones are to be regarded as ossifications in 

 the superficial temporal fasciae of the head, and presumably on that account are not to 

 be compared with any of the ordinary cranial bones of other Fishes. 



b 



