326 PEOF. T. W. BRIDGE ON THE MORPHOLOGY OF THE SKULL 



It may be remarked that the ratios exhibit a general 'agreement with those of the 

 larger of the two specimens in the Oxford University Museum [Lankester, I. c. p. 15], 

 except that their relative values are smaller, a fact due to the greater value of the 

 unit of measurement, that is, the head-length, in the former as compared with the 

 latter specimen. For the rest it may be said that my specimen had the usual black 

 colour of the Paraguayan specimens, and in the character of its skin-areas and 

 denticulated scales closely resembled the specimen described and figured by Lankester. 

 The cloaca was situated to the left of the medio-ventral line, and both the pectoral 

 and pelvic fins were supported by an axial skeleton in the form of an obviously- 

 segmented rod of cartilage. Exclusive of the cranial rib, the specimen had 54 pairs of 

 ribs, or one pair fewer than the specimens described by Bischoff and Hyrtl. Lastly, 

 it may be added that the specimen was a male, with the characteristic series of 

 villous processes along the postero-medial margins of its pelvic fins. 



The first detailed account of the structure of the skull of Lepidosiren paradoxa, and 

 certainly the most important, is that given by Bischoff in his well-known and copiously- 

 illustrated memoir [2] published in 1840. This was followed a few years later (1845) 

 by Hyrtl's monograph [18], which, however, contained but a single figure of the skull, 

 viz. a lateral view. Hyrtl corrected one or two errors in Bischoff's memoir, and 

 slightly modified the nomenclature of certain of the cranial elements, but otherwise 

 added little to our knowledge of the structure of the skull ; indeed, as he himself says, 

 " Die Schfidelknochen wurden von Bischoff so vollstandig abgehandelt, dass ich mich 

 hier nur in eine Aufzahlung, nicht in eine Beschreibung derselben einzulassen brauche " 

 (I. c. p. 013). Briihl [4] two years later (1847) reproduced several of Bischoff's 

 figures, and suggested certain modifications in the names of some of the cranial bones, 

 but in other respects his description is obviously based on the work of his distinguished 

 predecessor, 



The figures given in Bischoff's memoir, although for the most part accurate, 

 nevertheless justify the criticism that neither the shape nor the sutural boundaries 

 of the various bones are always represented with sufficient clearness, and are further 

 defective in that sufficient attention has not been given to the structure of the 

 chondrocranium. In several points the text also needs revision, more particularly in 

 the light of modern researches in cranial morphology. 



Of other Dipnoids, the cranial anatomy of Protopterus has perhaps been the more 

 fully treated. The first account by Owen [25] was very imperfect, but was revised and 

 certainly improved in his ' Comparative Anatomy and Physiology of Vertebrates ' [26]. 

 Peters [34], Huxley [14], and Cobbold [6] have also contributed to our knowledge of 

 the skull of this Dipnoid. It is to Wiedersheim [41], however, that we are indebted 

 for the best account of the skull of Protopterus, and his admirable paper has the 

 additional merit of being illustrated by excellent and accurate figures. 



