XIII 



PHYLUM CHORDATA 



259 



that of Amphibia (see Section XIV.) in the presence of long and 

 relatively narrow cerebral hemispheres, the nervous roof or pallium 

 of which contains a stratified layer of nerve-cells. In all the 

 Dipnoi the part of the hemisphere (olfactory lobe and tubercle) from 

 which the olfactory nerve-fibres pass to the bulbus olfactorius is 

 of relatively large size. In Protopterus and Lepidosiren the 

 olfactory tract is not distinguishable, bulbus and lobus being in 

 immediate apposition. In both these genera the dorsal part 

 of the mid-brain is undivided. In both genera the kidneys are 



FIG. 'Jl 4. Protopterus. Skull, shoulder-girdle, and skeleton of fore-limb. A, splemal : AF, 

 pre-orbital process ; a and b (on lower jaw), and S L, teeth ; b, basal eartilage of pectoral fin ; 

 B, ligamentous band connecting the mandible with the hyoid ; t-o. ligamentous band connecting 

 the dorsal end of the pectoral arch with the skull ; J), angular ; FP, fron to-parietal ; Ht, 

 membranous fenestra perforated by the foramen for the optic nerve (II); Hy. hyoid ; K, 

 external gills ; K n, Kn', cartilage of the pectoral arch ; KR, occipital rib ; LK and MK, investing 

 bones of the pectoral arch ; ./VA', olfactory capsule ; Ob, auditory capsule ; Occ. supraoccipital ; 

 Op. and Gp'. rudimentary opercular bones ; PQ palatoquadrate ; Psp. Psp'. spinous processes 

 of the anterior vertebrae ; UK supraethmoid bone ; SK, roofing membrane-bones ; Tr. palato- 

 quadrate cartilage ; WW, anterior vertebras coalescent with the skull ; I-V, branchial arches 

 (that marked / is forked and the anterior bar may represent the first, in which case there are 

 six branchial arches) ; 1,2, 3, segments of axis of pectoral fin ; *, *, vestigial lateral rays of 

 pectoral fin. (From Wiedersheim.) 



relatively more elongated than in Ceratodus; in Protopterus the 

 posterior portions are fused together ; in Lepidosiren they remain 

 separate throughout. In both genera the elongated testes are dis- 

 tinguishable into two regions an anterior longer, sperm-producing 

 part, and a posterior shorter part which serves as a duct and a 

 vesicula seminalis. In Lepidosiren about six vasa etferentia arise 

 from this posterior region and enter the Malpighian capsules of 

 the mesonephros : in Protopterus there is only a single vas 

 efferens. The ducts of the two kidneys open by a single aperture 

 (Protopterus) or two separate apertures on the summit of a 



