IN THE PARAGUAYAN LEPIDOSIREN, ETC. 345 



connected with the fibrous tissue of the base of the skull, no special ligamentous 

 attachments to the latter could be perceived. The first arch, which, in consequence 

 of the suppression of the hyoidean cleft, is in close proximity to the inner surface of 

 the hinder margin of the suspensorial cartilage, dorsad to the upper extremity of the 

 cerato-hyal, is the longest of the series, but very slender. The second is much 

 stouter, but shorter, slightly expanded at its ventral extremity, and bifurcate and 

 grooved at its dorsal end for the reception of the second aortic arch. The third is 

 somewhat more slender than the second, but thicker than the first or fourth, and is 

 neither grooved nor forked dorsally. The fourth and fifth resemble the third, but are 

 very slender, the fifth being much the shortest of the series. No trace of the two 

 basibranchial elements, described by Huxley (I. c.) as present in Ceratodus, or of the 

 epibranchial elements described by Ridewood [35 a] as existing in connection with the 

 second and third branchial arches in Protopterus, could be detected in Lepidosiren . 



It may be mentioned that, in consequence of the suppression of the hyoidean or hyo- 

 branchial cleft, the hyoidean hemibranch really projects into the cleft separating the 

 first and second branchial arches. 



The characteristic " cranial rib " of other Dipnoi is present also in Lepidosiren, and 

 was erroneously designated by Bischoff (I.e.)" Suspensoriu m der Schulter " (PL XXVIII . 

 figs. 1-4, c.r.). Its dorsal extremity is furnished with two rounded cartilaginous con- 

 dyles for articulation with a suitably-modified concavity in the chondrocranial cartilage 

 between the Vagus foramen in front and above, the exoccipital behind, and the lateral 

 edge of the parasphenoid below. Its extremities are cartilaginous, but the rest 

 of its extent consists of an axial core of cartilage invested by a relatively thick 

 bony sheath. Morphologically, it may be considered to represent the costal element 

 pertaining to the first neural arch. 



The attachment of the dorsal extremity of each lateral half of the pectoral girdle 

 to the skull is effected by a stout ligament which extends from the postero-lateral 

 portion of the cranium, behind and a little dorsad to the Vagus foramen, and is inserted 

 into the upper extremity of the supraclavicle. There is apparently no representative 

 of the " post-temporal " of Protopterus and Ceratodus. 



The only account of the cranial nerves of Lepidosiren (L. paradoxa, Fitz.) is that 

 given by Hyrtl (/. c), whose description, in so far as the course and distribution of the 

 larger branches are concerned, is in the main accurate, although characterized by the 

 defect that the author has not always been successful in discriminating between the 

 branches of the Facialis and those of the Trigeminus. In order to ascertain their 

 relations to the various cranial foramina, a careful investigation of the peripheral dis- 

 tribution of the various cranial nerves of the Paraguayan Lepidosiren was made, with the 

 result that my own observations proved to be in fairly close agreement with those pre- 

 viously recorded by Hyrtl, and more especially with the account given of the cranial 

 nerves of Protopterus annectens in a recent and admirable paper by Pinkus [25I. In 



