424 F/SUES. 



DIAGRAM XXVI. 

 Elasmobranchs. 



The Fig. named Skull (after W. K. Parker) shows the snout and 

 nasal capsules, with four pairs of labial cartilages (/'"*), the antorbital 

 cartilage [a. o. ), the palato-pterygo-quadrate {q. p. pt. ), Meckel's cartilage 

 (ct. c), the first hypo-branchial (h. br.'^\ the fifth hypo-branchial 

 {h. br.^), the cerato-hyal (c. hy.), the fifth pharyngo-branchial (p. br.^). 



The Fig. named Egg-case (after Giinther) shows a mermaid's purse. 



Brain shows the cerebral hemispheres (c. h. ) and the olfactory nerves, 

 the optic thalami (thai. ), the optic lobes (opt. ), the cerebellum (cereb. ), 

 the medulla oblongata (m. o.), the origin of the 2nd, 5th, and loth 

 nerves. * 



The Fig. Ext. gills (after W. K. Parker) shows the external gills on a 

 young skate. 



T^he disposition of the Gills is shown diagrammatically ; If., the hyoid 

 arch with half a gill, 1-4, the first four branchial arches each with a gill, 

 S, the fifth arch without any. 



Spiral (after Giinther) shows the spiral fold in the large intestine. 



Sect, (after J. T. Cunningham) represents a section of a segmented 

 ovum : — ep. the epiblast ; hy. the invaginated hypoblast ; me. (dark) the 

 mesoblast ; s. c. the segmentation cavity ; g. i. the gastrula cavity ; no. 

 (dark) the rudiment of the notochord ; the dotted line (z) suggests how 

 far the blastoderm has spread over the yolk. 



